0001104659-13-022847.txt : 20130321 0001104659-13-022847.hdr.sgml : 20130321 20130321114407 ACCESSION NUMBER: 0001104659-13-022847 CONFORMED SUBMISSION TYPE: 485BPOS PUBLIC DOCUMENT COUNT: 7 FILED AS OF DATE: 20130321 DATE AS OF CHANGE: 20130321 EFFECTIVENESS DATE: 20130321 FILER: COMPANY DATA: COMPANY CONFORMED NAME: MORGAN STANLEY MORTGAGE SECURITIES TRUST CENTRAL INDEX KEY: 0000806564 IRS NUMBER: 000000000 STATE OF INCORPORATION: MA FISCAL YEAR END: 1031 FILING VALUES: FORM TYPE: 485BPOS SEC ACT: 1933 Act SEC FILE NUMBER: 033-10363 FILM NUMBER: 13706857 BUSINESS ADDRESS: STREET 1: 522 FIFTH AVENUE CITY: NEW YORK STATE: NY ZIP: 10036 BUSINESS PHONE: 800-869-6397 MAIL ADDRESS: STREET 1: 522 FIFTH AVENUE CITY: NEW YORK STATE: NY ZIP: 10036 FORMER COMPANY: FORMER CONFORMED NAME: MORGAN STANLEY FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 20010618 FORMER COMPANY: FORMER CONFORMED NAME: MORGAN STANLEY DEAN WITTER FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 19980622 FORMER COMPANY: FORMER CONFORMED NAME: WITTER DEAN FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 19930210 FILER: COMPANY DATA: COMPANY CONFORMED NAME: MORGAN STANLEY MORTGAGE SECURITIES TRUST CENTRAL INDEX KEY: 0000806564 IRS NUMBER: 000000000 STATE OF INCORPORATION: MA FISCAL YEAR END: 1031 FILING VALUES: FORM TYPE: 485BPOS SEC ACT: 1940 Act SEC FILE NUMBER: 811-04917 FILM NUMBER: 13706858 BUSINESS ADDRESS: STREET 1: 522 FIFTH AVENUE CITY: NEW YORK STATE: NY ZIP: 10036 BUSINESS PHONE: 800-869-6397 MAIL ADDRESS: STREET 1: 522 FIFTH AVENUE CITY: NEW YORK STATE: NY ZIP: 10036 FORMER COMPANY: FORMER CONFORMED NAME: MORGAN STANLEY FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 20010618 FORMER COMPANY: FORMER CONFORMED NAME: MORGAN STANLEY DEAN WITTER FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 19980622 FORMER COMPANY: FORMER CONFORMED NAME: WITTER DEAN FEDERAL SECURITIES TRUST DATE OF NAME CHANGE: 19930210 0000806564 S000002467 Morgan Stanley Mortgage Securities Trust C000006611 A MTGAX C000006612 B MTGBX C000006613 L MTGCX C000006614 I MTGDX 485BPOS 1 a13-2937_6485bpos.htm 485BPOS

As filed with the Securities and Exchange Commission on March 21, 2013

Registration Nos.: 33-10363
811-4917

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT
  UNDER THE SECURITIES ACT OF 1933  
x

  Pre-Effective Amendment No.  o

  Post-Effective Amendment No. 35  x

and/or

  REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY
  ACT OF 1940  
x

  Amendment No. 36  x

Morgan Stanley Mortgage Securities Trust

(A Massachusetts business trust)

(Exact Name of Registrant as Specified in Charter)

522 Fifth Avenue
New York, New York 10036

(Address of Principal Executive Office)

Registrant's Telephone Number, Including Area Code: (212) 296-6970

Stefanie V. Chang Yu, Esq.
522 Fifth Avenue
New York, New York 10036

(Name and Address of Agent for Service)

Copy to:

        Carl Frischling, Esq.
Kramer Levin Naftalis & Frankel LLP
1177 Avenue of the Americas
New York, New York 10036
  Stuart M. Strauss, Esq.
Dechert LLP
1095 Avenue of the Americas
New York, New York 10036
 

Approximate Date of Proposed Public Offering:

As soon as practicable after this Post-Effective Amendment becomes effective.

It is proposed that this filing will become effective (check appropriate box)

         

X

   

Immediately upon filing pursuant to paragraph (b)

 
           

On (date) pursuant to paragraph (b)

 
           

60 days after filing pursuant to paragraph (a)(1)

 
           

On (date) pursuant to paragraph (a)(1)

 
           

75 days after filing pursuant to paragraph (a)(2)

 
           

On (date) pursuant to paragraph (a)(2) of Rule 485.

 

Amending the Prospectus and Updating Financial Statements

       

If appropriate, check the following box:

 
   

This post-effective amendment designates a new effective

 
   

date for a previously filed post-effective amendment.

 



 

SIGNATURES

 

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933, and has duly caused this Post-Effective Amendment to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York and State of New York on the 21st day of March 2013.

 

 

MORGAN STANLEY MORTGAGE SECURITIES TRUST

 

 

 

By:

 

/s/  Arthur lev

 

 

 

Arthur Lev

 

 

 

President and Principal Executive Officer

 

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 35 has been signed below by the following persons  in the capacities and on the dates indicated.

 

Signatures

 

Title

 

Date

(1) Principal Executive Officer

 

President and Principal

 

 

 

 

Executive Officer

 

 

 

 

 

 

 

By:

/s/  Arthur Lev

 

 

 

 

 

Arthur Lev

 

 

 

March 21, 2013

 

 

 

 

 

 

 

 

 

 

(2) Principal Financial Officer

 

Principal Financial Officer

 

 

 

 

 

 

 

 

 

 

 

 

By:

/s/  Francis J. Smith

 

 

 

 

 

Francis J. Smith

 

 

 

March 21, 2013

 

 

 

 

 

(3)  Majority of the Trustees

 

 

 

 

 

 

 

 

 

James F. Higgins

 

 

 

 

 

 

 

 

 

By:

/s/  Stefanie V. Chang Yu

 

 

 

 

 

Stefanie V. Chang Yu

 

 

 

 

 

Attorney-in-Fact

 

 

 

March 21, 2013

 

 

 

 

 

 

 

 

 

 

Frank L. Bowman

Michael F. Klein

 

 

 

 

Michael Bozic

Michael E. Nugent (Chairman)

 

 

 

 

Kathleen A. Dennis

W. Allen Reed

 

 

 

 

Manuel H. Johnson

Fergus Reid

 

 

 

 

Joseph J. Kearns

 

 

 

 

 

 

 

 

 

 

By:

/s/  Carl Frischling

 

 

 

 

 

Carl Frischling

 

 

 

 

 

Attorney-in-Fact

 

 

 

March 21, 2013

 


 


 

EXHIBIT INDEX

 

Index No.

 

Description of Exhibit

 

 

 

EX-101.INS

 

XBRL Instance Document

EX-101.SCH

 

XBRL Taxonomy Extension Schema Document

EX-101.CAL

 

XBRL Taxonomy Extension Calculation Linkbase

EX-101.DEF

 

XBRL Taxonomy Extension Definition Linkbase

EX-101.LAB

 

XBRL Taxonomy Extension Labels Linkbase

EX-101.PRE

 

XBRL Taxonomy Extension Presentation Linkbase

 

EX-101.INS 2 ck0000806564-20130228.xml XBRL INSTANCE DOCUMENT 0000806564 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:C000006611Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:C000006612Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:C000006613Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:C000006614Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member rr:AfterTaxesOnDistributionsMember ck0000806564:C000006611Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member rr:AfterTaxesOnDistributionsAndSalesMember ck0000806564:C000006611Member 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:index_Barclays_Capital_Mortgage_Index_reflects_no_deduction_for_fees_expenses_or_taxesMember 2012-10-31 2012-10-31 0000806564 ck0000806564:S000002467_46Member ck0000806564:S000002467Member ck0000806564:index_Lipper_US_Mortgage_Funds_Index_reflects_no_deduction_for_taxesMember 2012-10-31 2012-10-31 xbrli:pure iso4217:USD Effective February 25, 2013, Class C shares were renamed Class L shares. Investments that are not subject to any sales charges at the time of purchase are subject to a contingent deferred sales charge ("CDSC") of 1.00% that will be imposed if you sell your shares within 18 months after purchase, except for certain specific circumstances. The Class B CDSC is scaled down to 1.00% during the sixth year, reaching zero thereafter. See "Share Class Arrangements" for a complete discussion of the CDSC. The Board of Trustees approved an amendment to the Plan of Distribution reducing the distribution and shareholder services (12b-1) fee for the Fund's Class L shares from 0.85% to 0.50% of the average daily net assets of such Class, effective February 25, 2013. The Distribution and/or Shareholder Service (12b-1) Fee shown in the table above has been restated to reflect such change. The Fund's "Adviser," Morgan Stanley Investment Management Inc., and its "Administrator," Morgan Stanley Services Company Inc., have agreed to reduce its advisory fee, its administration fee and/or reimburse the Fund so that Total Annual Fund Operating Expenses, excluding brokerage fees and 12b-1 fees, will not exceed 0.75% for each Class. The fee waivers and/or expense reimbursements will continue for at least one year or until such time as the Fund's Board of Trustees acts to discontinue all or a portion of such waivers and/or reimbursements when it deems such action is appropriate. These returns do not reflect any tax consequences from a sale of your shares at the end of each period. Effective April 2005, Class B shares will generally convert to Class A shares approximately eight years after the end of the calendar month in which the shares were purchased. The "Past 10 Years" performance for Class B shares reflects this conversion. Effective February 25, 2013, Class C shares were renamed Class L shares. The one year performance of Class L shares reflects the 1% contingent deferred sales charge (CDSC) in effect for Class C shares as of December 31, 2012. Class C shares held for less than one year were subject to a 1% CDSC. The CDSC on Class L shares was eliminated effective February 25, 2013. The Barclays Capital Mortgage Index covers the mortgage-backed pass-through securities of Ginnie Mae (GNMA), Fannie Mae (FNMA), and Freddie Mac (FHLMC). This Index is the Mortgage Backed Securities Fixed Rate component of the Barclays Capital U.S. Aggregate Index. It is not possible to invest directly in an index. The Lipper U.S. Mortgage Funds Index is an equally weighted performance index of the largest qualifying funds (based on net assets) in the Lipper U.S. Mortgage Funds classification. There are currently 30 funds represented in this Index. MORGAN STANLEY MORTGAGE SECURITIES TRUST 485BPOS false 0000806564 2012-10-31 2013-02-28 2013-02-28 2013-02-28 Morgan Stanley Mortgage Securities Trust MTGAX MTGBX MTGCX MTGDX Investment Objective <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:10pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Morgan Stanley Mortgage Securities Trust (the "Fund") seeks a high level of current income.</font> </p> Fees and Expenses <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the Morgan Stanley Funds. More information about these and other discounts is available from your financial advisor and in the "Share Class Arrangements" section beginning on page 30 of this</font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><i>Prospectus</i></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">and in the "Purchase, Redemption and Pricing of Shares" section beginning on page 53 of the Fund's</font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><i>Statement of Additional Information ("SAI")</i></font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">.</font> </p> 0.0425 0.0000 0.0000 0.0000 0.0000 0.0500 0.0000 0.0000 0.0047 0.0047 0.0047 0.0047 0.0025 0.0085 0.0050 0.0000 0.0056 0.0056 0.0056 0.0056 0.0128 0.0188 0.0153 0.0103 -0.0028 -0.0028 -0.0028 -0.0028 0.0100 0.0160 0.0125 0.0075 ~ http://morganstanley.com/20130228/role/ScheduleShareholderFees20001 column dei_LegalEntityAxis compact ck0000806564_S000002467Member row primary compact * ~ ~ http://morganstanley.com/20130228/role/ScheduleAnnualFundOperatingExpenses20002 column dei_LegalEntityAxis compact ck0000806564_S000002467Member row primary compact * ~ You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the Morgan Stanley Funds. Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) Investments that are not subject to any sales charges at the time of purchase are subject to a contingent deferred sales charge ("CDSC") of 1.00% that will be imposed if you sell your shares within 18 months after purchase, except for certain specific circumstances. The Class B CDSC is scaled down to 1.00% during the sixth year, reaching zero thereafter. See "Share Class Arrangements" for a complete discussion of the CDSC. 25000 Shareholder Fees (fees paid directly from your investment) Example <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.</font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The example assumes that you invest $10,000 in the Fund, your investment has a 5% return each year, and the Fund's operating expenses remain the same (except for the ten-year amounts for Class B shares which reflect the conversion to Class A shares eight years after the end of the calendar month in which the shares were purchased). Although your actual costs may be higher or lower, based on these assumptions your costs would be:</font> </p> 523 730 954 1598 663 805 1071 1740 127 397 686 1511 77 240 417 930 523 730 954 1598 163 505 871 1740 127 397 686 1511 77 240 417 930 ~ http://morganstanley.com/20130228/role/ScheduleExpenseExampleTransposed20003 column dei_LegalEntityAxis compact ck0000806564_S000002467Member row primary compact * ~ ~ http://morganstanley.com/20130228/role/ScheduleExpenseExampleNoRedemptionTransposed20004 column dei_LegalEntityAxis compact ck0000806564_S000002467Member row primary compact * ~ If You SOLD Your Shares: If You HELD Your Shares: Past Performance <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's Class A shares' performance from year-to-year and by showing how the Fund's average annual returns for the one, five and 10 year periods compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time. The performance of the other Classes will differ because the Classes have different ongoing fees. The performance information in the bar chart does not reflect the deduction of sales charges; if these amounts were reflected, returns would be less than shown. The Fund's returns in the table include the maximum applicable sales charge for each Class and assume you sold your shares at the end of each period (unless otherwise noted). The Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available online at www.morganstanley.com/im or by calling toll-free (800) 869-NEWS.</font> </p> Annual Total Returns-Calendar Years* 0.0184 0.0382 0.0231 0.0349 0.0520 -0.0864 0.0705 0.0589 0.0571 0.0841 ~ http://morganstanley.com/20130228/role/ScheduleAnnualTotalReturnsBarChart20005 column dei_LegalEntityAxis compact ck0000806564_S000002467Member row primary compact * ~ High Quarter 0.0385 2012-09-30 Low Quarter -0.0475 2008-03-31 <table style="width: 100%;" border="0" cellspacing="0" cellpadding="0"> <tr> <td style="padding: 0pt .7pt 0pt 0pt;" colspan="3" align="left" valign="bottom" width="65"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 8pt; font-family: Arial, Helvetica;"><strong>High Quarter</strong></font> </p> </td> <td colspan="1"> &#160; </td> <td style="padding: 0pt .7pt 0pt 0pt;" colspan="3" align="left" valign="bottom" width="47"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">9/30/12</font> </p> </td> <td colspan="1"> &#160; </td> <td style="padding: 0pt .7pt 0pt 0pt;" colspan="1" valign="bottom" width="8"> &#160; </td> <td style="padding: 0pt .7pt 0pt 0pt;" colspan="1" align="right" valign="bottom" width="38"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">3.85</font> </p> </td> <td style="padding: 0pt .7pt 0pt 0pt;" colspan="1" align="left" valign="bottom" width="24"> <p style="margin: 0pt 0pt 0pt 0pt; white-space: nowrap;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">%</font> </p> </td> <td colspan="1" width="8"> &#160; </td> </tr> <tr> <td style="padding: 0pt .7pt 6pt 0pt;" colspan="3" align="left" valign="bottom" width="65"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 8pt; font-family: Arial, Helvetica;"><strong>Low Quarter</strong></font> </p> </td> <td colspan="1"> &#160; </td> <td style="padding: 0pt .7pt 6pt 0pt;" colspan="3" align="left" valign="bottom" width="47"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">3/31/08</font> </p> </td> <td colspan="1"> &#160; </td> <td style="padding: 0pt .7pt 6pt 0pt;" colspan="1" valign="bottom" width="8"> &#160; </td> <td style="padding: 0pt .7pt 6pt 0pt;" colspan="1" align="right" valign="bottom" width="38"> <p style="margin: 0pt 0pt 0pt 0pt;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8211;4.75</font> </p> </td> <td style="padding: 0pt .7pt 6pt 0pt;" colspan="1" align="left" valign="bottom" width="24"> <p style="margin: 0pt 0pt 0pt 0pt; white-space: nowrap;"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">%</font> </p> </td> <td colspan="1" width="8"> &#160; </td> </tr> </table> <p style="margin: 2.5pt 0pt 6pt 0pt;" align="left"> <font style="font-size: 8pt; font-family: Arial, Helvetica;"><em>*&#160;&#160;The Fund previously disclosed the total return of Class B shares. However, Class B shares are closed to new investments. The bar chart now shows Class A shares which remain open to new investments.</em></font> </p> 0.0380 0.0259 0.0295 0.0246 0.0129 0.0149 0.0245 0.0142 0.0163 0.0291 0.0253 0.0288 0.0691 0.0291 0.0278 0.0874 0.0378 0.0366 0.0259 0.0567 0.0508 0.0460 0.0556 0.0460 ~ http://morganstanley.com/20130228/role/ScheduleAverageAnnualReturnsTransposed20006 column dei_LegalEntityAxis compact ck0000806564_S000002467Member column rr_PerformanceMeasureAxis compact * row primary compact * ~ <p style="margin: 0pt 0pt 6pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes. After-tax returns for the Fund's other Classes will vary from the Class A shares' returns. Actual <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable.</font><br /> </font> </p> The Fund's returns in the table include the maximum applicable sales charge for each Class and assume you sold your shares at the end of each period (unless otherwise noted). The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes. The Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future. The performance information in the bar chart does not reflect the deduction of sales charges; if these amounts were reflected, returns would be less than shown. www.morganstanley.com/im Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's Class A shares' performance from year-to-year and by showing how the Fund's average annual returns for the one, five and 10 year periods compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time. After-tax returns for the Fund's other Classes will vary from the Class A shares' returns. (reflects no deduction for fees, expenses or taxes) After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable. (800) 869-NEWS Average Annual Total Returns For Periods Ended December 31, 2012 The Fund previously disclosed the total return of Class B shares. However, Class B shares are closed to new investments. The bar chart now shows Class A shares which remain open to new investments. Portfolio Turnover <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The Fund pays transaction costs when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Total Annual Fund Operating Expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 238% of the average value of its portfolio.</font> </p> 2.38 Principal Risks <p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">There is no assurance that the Fund will achieve its investment objective and you can lose money investing in this Fund. The principal risks of investing in the Fund include:</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>Fixed-Income Securities.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Fixed-income securities are subject to the risk of the issuer's inability to meet principal and interest payments on its obligations (i.e., credit risk) and are subject to price volatility resulting from, among other things, interest rate sensitivity, market perception of the creditworthiness of the issuer and general market liquidity (i.e., market risk). The Fund is not limited as to the maturities of the securities in which it may invest. Securities with longer durations are likely to be more sensitive to changes in interest rates, generally making them more volatile than securities with shorter durations. Lower rated fixed-income securities have greater volatility because there is less certainty that principal and interest payments will be made as scheduled.</font> </p> <br/><p style="margin: 0pt 0pt 4pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><strong><em>Mortgage-Backed Securities.</em></strong></font> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Mortgage-backed securities entail prepayment risk, which generally increases during a <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">period of falling interest rates. Rising interest rates tend to discourage refinancings, with the result that the average life and volatility of mortgage securities will increase and market price will decrease. Rates of prepayment, faster or slower than expected by the Adviser, could reduce the Fund's yield, increase the volatility of the Fund and/or cause a decline in net asset value. Certain mortgage-backed securities may be more volatile and less liquid than other traditional types of debt securities. In addition, an unexpectedly high rate of defaults on the mortgages held by a mortgage pool may adversely affect the value of a mortgage-backed security and could result in losses to the Fund. The risk of such defaults is generally higher in the case of mortgage pools that include sub-prime mortgages. In addition, the Fund may invest in to-be-announced pass-through mortgage securities, which settle on a delayed delivery basis ("TBAs"). Investments in TBAs may give rise to a form of leverage and may cause the Fund's portfolio turnover rate to appear higher. Leverage may cause the fund to be more volatile than if the Fund had not been leveraged.</font><br /> </font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>CMOs.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">CMOs are comprised of various tranches, the expected cash flows on which have varying degrees of predictability as compared with the underlying Mortgage Assets. The less predictable the cash flow, the higher the yield and the greater the risk. In addition, if the collateral securing CMOs or any third-party guarantees are insufficient to make payments, the Fund could sustain a loss.</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>SMBS.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Investments in each class SMBS are extremely sensitive to changes in interest rates. IOs tend to decrease in value substantially if interest rates decline and prepayment rates become more rapid. POs tend to decrease in value substantially if interest rates increase and the rate of prepayment decreases. If the Fund invests in SMBS and interest rates move in a manner not anticipated by Fund management, it is possible that the Fund could lose all or substantially all of its investment.</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>CMBS.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">CMBS are subject to credit risk and prepayment risk. Although prepayment risk is present, it is of a lesser degree in CMBS than in the residential mortgage market; commercial real estate property loans often contain provisions which substantially reduce the likelihood that such securities will be prepaid (e.g., significant prepayment penalties on loans and, in some cases, prohibition on principal payments for several years following origination).</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>Inverse Floaters.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Like most other fixed-income securities, the value of inverse floaters will decrease as interest rates increase. They are more volatile, however, than most other fixed-income securities because the coupon rate on an inverse floater typically changes at a multiple of the change in the relevant index rate. Thus, any rise in the index rate (as a consequence of an increase in interest rates) causes a correspondingly greater drop in the coupon rate of an inverse floater while a drop in the index rate causes a correspondingly greater increase in the coupon rate of an inverse floater. Some inverse floaters may also increase or decrease substantially because of changes in the rate of prepayments.</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>U.S. Government Securities.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The U.S. government securities in which the Fund invests can be subject to two types of risk: credit risk and interest rate risk. When the general level of interest rates goes up, the prices of most fixed-income securities go down. When the general level of interest rates goes down, the prices of most fixed-income securities go up. While the credit risk associated with U.S. government securities generally is considered to be minimal, the interest rate risk can be substantial. With respect to U.S. government securities that are not backed by the full faith and credit of the U.S. Government, there is the risk that the U.S. Government will not provide financial support to such U.S. government agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law.</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>Asset-Backed Securities.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Asset-backed securities involve the risk that various federal and state consumer laws and other legal and economic factors may result in the collateral backing the securities being insufficient to support payment on the securities. Asset-backed securities also have risk characteristics similar to mortgage-backed securities.</font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;</font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>Liquidity Risk.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The Fund's investments in restricted and illiquid securities may entail greater risk than investments in publicly traded securities. These securities may be more difficult to sell, particularly in times of market turmoil. Illiquid securities may be more difficult to value. If the Fund is forced to sell an illiquid security to fund redemptions or for other cash needs, it may be forced to sell the security at a loss.</font> </p> <br/><p style="margin: 0pt 0pt 4pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><strong><em>&#8226; High Yield Securities ("Junk Bonds").</em></strong></font> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The prices of these securities are likely to be more sensitive to adverse economic changes, resulting in increased volatility of market prices of these securities during periods of economic uncertainty, or adverse individual corporate developments, than higher-rated securities. In addition, during an economic downturn or <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">substantial period of rising interest rates, junk bond issuers and, in particular, highly leveraged issuers may experience financial stress and an increased incidence of default. In the event of a default, the Fund may incur additional expenses to seek recovery.</font><br /> </font> </p> <br/><p style="margin:0pt 0pt 4pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><b><i>Foreign Securities.</i></b></font> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Investments in foreign markets entail special risks such as currency, political, economic and market risks. There also may be greater market volatility, less reliable financial information, higher transaction and custody costs, decreased market liquidity and less government and exchange regulation associated with investments in foreign markets. In addition, investments in certain foreign markets, which have historically been considered stable, may become more volatile and subject to increased risk due to ongoing developments and changing conditions in such markets. Moreover, the growing interconnectivity of global economies and financial markets has increased probability that adverse developments and conditions in one country or region will affect the stability of economies and financial markets in other countries or regions. In addition, the Fund's investments may be denominated in foreign currencies and therefore, to the extent unhedged, the value of the investment will fluctuate with the U.S. dollar exchange rates. To the extent hedged by use of foreign currency forward exchange contracts, the precise matching of foreign currency forward exchange contract amounts and the value of the securities involved will not generally be possible because the future value of such securities in foreign currencies will change as a consequence of market movements in the value of those securities between the date on which the contract is entered into and the date it matures. There is additional risk that such transactions reduce or preclude the opportunity for gain if the value of the currency should move in the direction opposite to the position taken and that foreign currency forward exchange contracts create exposure to currencies in which the Fund's securities are not denominated. The use of foreign currency forward exchange contracts involves the risk of loss from the insolvency or bankruptcy of the counterparty to the contract or the failure of the counterparty to make payments or otherwise comply with the terms of the contract.</font> </p> <br/><p style="margin: 0pt 0pt 4pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">&#8226;&#160;&#160;</font><font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;"><strong><em>Derivatives.</em></strong></font> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">A derivative instrument often has risks similar to its underlying asset and may have additional risks, including imperfect correlation between the value of the derivative and the underlying asset, risks of default by the other party to certain transactions, magnification of losses incurred due to changes in the market value of the securities, <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">instruments, indices or interest rates to which they relate, and risks that the transactions may not be liquid. Certain derivative transactions may give rise to a form of leverage. Leverage magnifies the potential for gain and the risk of loss.</font><br /> </font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency.</font> </p> There is no assurance that the Fund will achieve its investment objective and you can lose money investing in this Fund. Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency. Principal Investment Strategies <p style="margin: 0pt 0pt 6pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The Fund normally invests at least 80% of its assets in mortgage-related securities. These mortgage-related securities may include mortgage-backed securities such as mortgage pass-through securities, collateralized mortgage obligations ("CMOs"), stripped mortgage-backed securities ("SMBS"), commercial mortgage-backed securities ("CMBS") and inverse floating rate obligations ("inverse floaters"). In making investment decisions, the Adviser considers economic developments, interest rate levels and other factors. The Fund may invest in high yield securities (commonly referred to as <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">"junk bonds"). The Fund is not limited as to the maturities or types of mortgage-backed securities in which it may invest.</font><br /> </font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">One type of mortgage-backed security in which the Fund may invest is a mortgage pass-through security, which represents a participation interest in a pool of residential mortgage loans originated by U.S. governmental or private lenders such as banks. Mortgage pass-through securities provide for monthly payments that are a "pass-through" of the monthly interest and principal payments made by the individual borrowers on the pooled mortgage loans. CMOs are debt obligations collateralized by mortgage loans or mortgage pass-through securities (collectively "Mortgage Assets"). CMOs are issued in multiple classes and each class has a fixed or floating rate and a stated maturity or final distribution date. Certain classes will have more predictable cash flows than others. The Fund may invest in any class of CMO. SMBS are derivative multi-class mortgage securities. A common type of stripped mortgage security will have one class receiving some of the interest and most of the principal from the Mortgage Assets, while the other class receives most of the interest and the remainder of the principal. In the most extreme case, one class will receive all of the interest (the interest-only or "IO" class), while the other class will receive all of the principal (the principal-only or "PO" class). CMBS are generally multi-class or pass-through securities backed by a mortgage loan or a pool of mortgage loans secured by commercial property, such as industrial and warehouse properties, office buildings, retail space and shopping malls, multifamily properties and cooperative apartments. Inverse floaters are obligations which pay interest at rates that vary inversely with changes in market rates of interest. Because the interest rate paid to holders of such obligations is generally determined by subtracting a variable or floating rate from a predetermined amount, the interest rate paid to holders of such obligations will decrease as such variable or floating rate increases and increase as such variable or floating rate decreases.</font> </p> <br/><p style="margin: 0pt 0pt 6pt 0pt;" align="left"> <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">In many cases, the mortgage-backed securities in which the Fund invests will be U.S. government securities (including zero coupon securities). The Fund also may invest in other U.S. government securities, including, but not limited to, U.S. Treasury bills, notes and bonds, securities (including mortgage-backed securities) issued by agencies and instrumentalities of the U.S. Government which may or may not be backed by the full faith and credit of the United States, and securities issued <font style="font-size: 9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">by agencies and instrumentalities which are backed solely by the credit of the issuing agency or instrumentality.</font><br /> </font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The Fund may also invest in asset-backed securities and restricted and illiquid securities.</font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">In addition, the Fund may invest up to 10% of its assets in foreign securities, including U.S. dollar-denominated securities issued in the U.S. capital markets by foreign issuers, some of which are commonly known as "Yankee Bonds" and non-U.S. dollar-denominated securities, including Eurobonds.</font> </p> <br/><p style="margin:0pt 0pt 6pt 0pt;" align="left"> <font style="font-size:9pt; font-family: Times New Roman PS Std, Times New Roman PS, Times New Roman, Times;">The Fund may, but it is not required to, use derivative instruments for a variety of purposes, including hedging, risk management, portfolio management or to earn income. The Fund's use of derivatives may involve the purchase and sale of derivative instruments such as futures, options, swaps and other related instruments and techniques. The Fund may utilize foreign currency forward exchange contracts, which are also derivatives, in connection with its investments in foreign securities. These derivative instruments will be counted toward the Fund's 80% policy discussed above to the extent they have economic characteristics similar to the securities included within that policy.</font> </p> EX-101.SCH 3 ck0000806564-20130228.xsd XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT 000001 - Document - Document and Entity Information link:presentationLink link:definitionLink link:calculationLink 020000 - Document - Risk/Return Summary {Unlabeled} - Morgan Stanley Mortgage Securities Trust link:presentationLink link:definitionLink link:calculationLink 020001 - Schedule - Shareholder Fees link:presentationLink link:definitionLink link:calculationLink 020002 - Schedule - Annual Fund Operating Expenses link:presentationLink link:definitionLink link:calculationLink 020003 - Schedule - Expense Example {Transposed} link:presentationLink link:definitionLink link:calculationLink 020004 - Schedule - Expense Example No Redemption {Transposed} link:presentationLink link:definitionLink link:calculationLink 020005 - Schedule - Annual Total Returns [Bar Chart] link:presentationLink link:definitionLink link:calculationLink 020006 - Schedule - Average Annual Returns {Transposed} link:presentationLink link:definitionLink link:calculationLink 020007 - Disclosure - Risk/Return Detail Data {Elements} - Morgan Stanley Mortgage Securities Trust link:presentationLink link:definitionLink link:calculationLink EX-101.LAB 4 ck0000806564-20130228_lab.xml XBRL TAXONOMY EXTENSION LABELS LINKBASE DOCUMENT EX-101.DEF 5 ck0000806564-20130228_def.xml XBRL TAXONOMY EXTENSION DEFINITION LINKBASE DOCUMENT EX-101.PRE 6 ck0000806564-20130228_pre.xml XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT EX-101.CAL 7 ck0000806564-20130228_cal.xml XBRL TAXONOMY EXTENSION CALCULATION LINKBASE DOCUMENT XML 8 report.css IDEA: XBRL DOCUMENT /* Updated 2009-11-04 */ /* v2.2.0.24 */ /* DefRef Styles */ ..report table.authRefData{ background-color: #def; border: 2px solid #2F4497; font-size: 1em; position: absolute; } ..report table.authRefData a { display: block; font-weight: bold; } ..report table.authRefData p { margin-top: 0px; } ..report table.authRefData .hide { background-color: #2F4497; padding: 1px 3px 0px 0px; text-align: right; } ..report table.authRefData .hide a:hover { background-color: #2F4497; } ..report table.authRefData .body { height: 150px; overflow: auto; width: 400px; } ..report table.authRefData table{ font-size: 1em; } /* Report Styles */ ..pl a, .pl a:visited { color: black; text-decoration: none; } /* table */ ..report { background-color: white; border: 2px solid #acf; clear: both; color: black; font: normal 8pt Helvetica, Arial, san-serif; margin-bottom: 2em; } ..report hr { border: 1px solid #acf; } /* Top labels */ ..report th { background-color: #acf; color: black; font-weight: bold; text-align: center; } ..report th.void { background-color: transparent; color: #000000; font: bold 10pt Helvetica, Arial, san-serif; text-align: left; } ..report .pl { text-align: left; vertical-align: top; white-space: normal; width: 200px; word-wrap: break-word; } ..report td.pl a.a { cursor: pointer; display: block; width: 200px; } ..report td.pl div.a { width: 200px; } ..report td.pl a:hover { background-color: #ffc; } /* Header rows... */ ..report tr.rh { background-color: #acf; color: black; font-weight: bold; } /* Calendars... */ ..report .rc { background-color: #f0f0f0; } /* Even rows... */ ..report .re, .report .reu { background-color: #def; } ..report .reu td { border-bottom: 1px solid black; } /* Odd rows... */ ..report .ro, .report .rou { background-color: white; } ..report .rou td { border-bottom: 1px solid black; } ..report .rou table td, .report .reu table td { border-bottom: 0px solid black; } /* styles for footnote marker */ ..report .fn { white-space: nowrap; } /* styles for numeric types */ ..report .num, .report .nump { text-align: right; white-space: nowrap; } ..report .nump { padding-left: 2em; } ..report .nump { padding: 0px 0.4em 0px 2em; } /* styles for text types */ ..report .text { text-align: left; white-space: normal; } ..report .text .big { margin-bottom: 1em; width: 17em; } ..report .text .more { display: none; } ..report .text .note { font-style: italic; font-weight: bold; } ..report .text .small { width: 10em; } ..report sup { font-style: italic; } ..report .outerFootnotes { font-size: 1em; } XML 9 R9.htm IDEA: XBRL DOCUMENT v2.4.0.6
Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Morgan Stanley Mortgage Securities Trust
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Morgan Stanley Mortgage Securities Trust (the "Fund") seeks a high level of current income.

Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the Morgan Stanley Funds. More information about these and other discounts is available from your financial advisor and in the "Share Class Arrangements" section beginning on page 30 of this Prospectus and in the "Purchase, Redemption and Pricing of Shares" section beginning on page 53 of the Fund's Statement of Additional Information ("SAI").

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Total Annual Fund Operating Expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 238% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 238.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock Investments that are not subject to any sales charges at the time of purchase are subject to a contingent deferred sales charge ("CDSC") of 1.00% that will be imposed if you sell your shares within 18 months after purchase, except for certain specific circumstances.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the Morgan Stanley Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 25,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.


The example assumes that you invest $10,000 in the Fund, your investment has a 5% return each year, and the Fund's operating expenses remain the same (except for the ten-year amounts for Class B shares which reflect the conversion to Class A shares eight years after the end of the calendar month in which the shares were purchased). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If You SOLD Your Shares:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If You HELD Your Shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund normally invests at least 80% of its assets in mortgage-related securities. These mortgage-related securities may include mortgage-backed securities such as mortgage pass-through securities, collateralized mortgage obligations ("CMOs"), stripped mortgage-backed securities ("SMBS"), commercial mortgage-backed securities ("CMBS") and inverse floating rate obligations ("inverse floaters"). In making investment decisions, the Adviser considers economic developments, interest rate levels and other factors. The Fund may invest in high yield securities (commonly referred to as "junk bonds"). The Fund is not limited as to the maturities or types of mortgage-backed securities in which it may invest.


One type of mortgage-backed security in which the Fund may invest is a mortgage pass-through security, which represents a participation interest in a pool of residential mortgage loans originated by U.S. governmental or private lenders such as banks. Mortgage pass-through securities provide for monthly payments that are a "pass-through" of the monthly interest and principal payments made by the individual borrowers on the pooled mortgage loans. CMOs are debt obligations collateralized by mortgage loans or mortgage pass-through securities (collectively "Mortgage Assets"). CMOs are issued in multiple classes and each class has a fixed or floating rate and a stated maturity or final distribution date. Certain classes will have more predictable cash flows than others. The Fund may invest in any class of CMO. SMBS are derivative multi-class mortgage securities. A common type of stripped mortgage security will have one class receiving some of the interest and most of the principal from the Mortgage Assets, while the other class receives most of the interest and the remainder of the principal. In the most extreme case, one class will receive all of the interest (the interest-only or "IO" class), while the other class will receive all of the principal (the principal-only or "PO" class). CMBS are generally multi-class or pass-through securities backed by a mortgage loan or a pool of mortgage loans secured by commercial property, such as industrial and warehouse properties, office buildings, retail space and shopping malls, multifamily properties and cooperative apartments. Inverse floaters are obligations which pay interest at rates that vary inversely with changes in market rates of interest. Because the interest rate paid to holders of such obligations is generally determined by subtracting a variable or floating rate from a predetermined amount, the interest rate paid to holders of such obligations will decrease as such variable or floating rate increases and increase as such variable or floating rate decreases.


In many cases, the mortgage-backed securities in which the Fund invests will be U.S. government securities (including zero coupon securities). The Fund also may invest in other U.S. government securities, including, but not limited to, U.S. Treasury bills, notes and bonds, securities (including mortgage-backed securities) issued by agencies and instrumentalities of the U.S. Government which may or may not be backed by the full faith and credit of the United States, and securities issued by agencies and instrumentalities which are backed solely by the credit of the issuing agency or instrumentality.


The Fund may also invest in asset-backed securities and restricted and illiquid securities.


In addition, the Fund may invest up to 10% of its assets in foreign securities, including U.S. dollar-denominated securities issued in the U.S. capital markets by foreign issuers, some of which are commonly known as "Yankee Bonds" and non-U.S. dollar-denominated securities, including Eurobonds.


The Fund may, but it is not required to, use derivative instruments for a variety of purposes, including hedging, risk management, portfolio management or to earn income. The Fund's use of derivatives may involve the purchase and sale of derivative instruments such as futures, options, swaps and other related instruments and techniques. The Fund may utilize foreign currency forward exchange contracts, which are also derivatives, in connection with its investments in foreign securities. These derivative instruments will be counted toward the Fund's 80% policy discussed above to the extent they have economic characteristics similar to the securities included within that policy.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

There is no assurance that the Fund will achieve its investment objective and you can lose money investing in this Fund. The principal risks of investing in the Fund include:


•  Fixed-Income Securities. Fixed-income securities are subject to the risk of the issuer's inability to meet principal and interest payments on its obligations (i.e., credit risk) and are subject to price volatility resulting from, among other things, interest rate sensitivity, market perception of the creditworthiness of the issuer and general market liquidity (i.e., market risk). The Fund is not limited as to the maturities of the securities in which it may invest. Securities with longer durations are likely to be more sensitive to changes in interest rates, generally making them more volatile than securities with shorter durations. Lower rated fixed-income securities have greater volatility because there is less certainty that principal and interest payments will be made as scheduled.


•  Mortgage-Backed Securities. Mortgage-backed securities entail prepayment risk, which generally increases during a period of falling interest rates. Rising interest rates tend to discourage refinancings, with the result that the average life and volatility of mortgage securities will increase and market price will decrease. Rates of prepayment, faster or slower than expected by the Adviser, could reduce the Fund's yield, increase the volatility of the Fund and/or cause a decline in net asset value. Certain mortgage-backed securities may be more volatile and less liquid than other traditional types of debt securities. In addition, an unexpectedly high rate of defaults on the mortgages held by a mortgage pool may adversely affect the value of a mortgage-backed security and could result in losses to the Fund. The risk of such defaults is generally higher in the case of mortgage pools that include sub-prime mortgages. In addition, the Fund may invest in to-be-announced pass-through mortgage securities, which settle on a delayed delivery basis ("TBAs"). Investments in TBAs may give rise to a form of leverage and may cause the Fund's portfolio turnover rate to appear higher. Leverage may cause the fund to be more volatile than if the Fund had not been leveraged.


•  CMOs. CMOs are comprised of various tranches, the expected cash flows on which have varying degrees of predictability as compared with the underlying Mortgage Assets. The less predictable the cash flow, the higher the yield and the greater the risk. In addition, if the collateral securing CMOs or any third-party guarantees are insufficient to make payments, the Fund could sustain a loss.


•  SMBS. Investments in each class SMBS are extremely sensitive to changes in interest rates. IOs tend to decrease in value substantially if interest rates decline and prepayment rates become more rapid. POs tend to decrease in value substantially if interest rates increase and the rate of prepayment decreases. If the Fund invests in SMBS and interest rates move in a manner not anticipated by Fund management, it is possible that the Fund could lose all or substantially all of its investment.


•  CMBS. CMBS are subject to credit risk and prepayment risk. Although prepayment risk is present, it is of a lesser degree in CMBS than in the residential mortgage market; commercial real estate property loans often contain provisions which substantially reduce the likelihood that such securities will be prepaid (e.g., significant prepayment penalties on loans and, in some cases, prohibition on principal payments for several years following origination).


•  Inverse Floaters. Like most other fixed-income securities, the value of inverse floaters will decrease as interest rates increase. They are more volatile, however, than most other fixed-income securities because the coupon rate on an inverse floater typically changes at a multiple of the change in the relevant index rate. Thus, any rise in the index rate (as a consequence of an increase in interest rates) causes a correspondingly greater drop in the coupon rate of an inverse floater while a drop in the index rate causes a correspondingly greater increase in the coupon rate of an inverse floater. Some inverse floaters may also increase or decrease substantially because of changes in the rate of prepayments.


•  U.S. Government Securities. The U.S. government securities in which the Fund invests can be subject to two types of risk: credit risk and interest rate risk. When the general level of interest rates goes up, the prices of most fixed-income securities go down. When the general level of interest rates goes down, the prices of most fixed-income securities go up. While the credit risk associated with U.S. government securities generally is considered to be minimal, the interest rate risk can be substantial. With respect to U.S. government securities that are not backed by the full faith and credit of the U.S. Government, there is the risk that the U.S. Government will not provide financial support to such U.S. government agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law.


•  Asset-Backed Securities. Asset-backed securities involve the risk that various federal and state consumer laws and other legal and economic factors may result in the collateral backing the securities being insufficient to support payment on the securities. Asset-backed securities also have risk characteristics similar to mortgage-backed securities.


Liquidity Risk. The Fund's investments in restricted and illiquid securities may entail greater risk than investments in publicly traded securities. These securities may be more difficult to sell, particularly in times of market turmoil. Illiquid securities may be more difficult to value. If the Fund is forced to sell an illiquid security to fund redemptions or for other cash needs, it may be forced to sell the security at a loss.


• High Yield Securities ("Junk Bonds"). The prices of these securities are likely to be more sensitive to adverse economic changes, resulting in increased volatility of market prices of these securities during periods of economic uncertainty, or adverse individual corporate developments, than higher-rated securities. In addition, during an economic downturn or substantial period of rising interest rates, junk bond issuers and, in particular, highly leveraged issuers may experience financial stress and an increased incidence of default. In the event of a default, the Fund may incur additional expenses to seek recovery.


•  Foreign Securities. Investments in foreign markets entail special risks such as currency, political, economic and market risks. There also may be greater market volatility, less reliable financial information, higher transaction and custody costs, decreased market liquidity and less government and exchange regulation associated with investments in foreign markets. In addition, investments in certain foreign markets, which have historically been considered stable, may become more volatile and subject to increased risk due to ongoing developments and changing conditions in such markets. Moreover, the growing interconnectivity of global economies and financial markets has increased probability that adverse developments and conditions in one country or region will affect the stability of economies and financial markets in other countries or regions. In addition, the Fund's investments may be denominated in foreign currencies and therefore, to the extent unhedged, the value of the investment will fluctuate with the U.S. dollar exchange rates. To the extent hedged by use of foreign currency forward exchange contracts, the precise matching of foreign currency forward exchange contract amounts and the value of the securities involved will not generally be possible because the future value of such securities in foreign currencies will change as a consequence of market movements in the value of those securities between the date on which the contract is entered into and the date it matures. There is additional risk that such transactions reduce or preclude the opportunity for gain if the value of the currency should move in the direction opposite to the position taken and that foreign currency forward exchange contracts create exposure to currencies in which the Fund's securities are not denominated. The use of foreign currency forward exchange contracts involves the risk of loss from the insolvency or bankruptcy of the counterparty to the contract or the failure of the counterparty to make payments or otherwise comply with the terms of the contract.


•  Derivatives. A derivative instrument often has risks similar to its underlying asset and may have additional risks, including imperfect correlation between the value of the derivative and the underlying asset, risks of default by the other party to certain transactions, magnification of losses incurred due to changes in the market value of the securities, instruments, indices or interest rates to which they relate, and risks that the transactions may not be liquid. Certain derivative transactions may give rise to a form of leverage. Leverage magnifies the potential for gain and the risk of loss.


Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency.

Risk Lose Money [Text] rr_RiskLoseMoney There is no assurance that the Fund will achieve its investment objective and you can lose money investing in this Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation ("FDIC") or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's Class A shares' performance from year-to-year and by showing how the Fund's average annual returns for the one, five and 10 year periods compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time. The performance of the other Classes will differ because the Classes have different ongoing fees. The performance information in the bar chart does not reflect the deduction of sales charges; if these amounts were reflected, returns would be less than shown. The Fund's returns in the table include the maximum applicable sales charge for each Class and assume you sold your shares at the end of each period (unless otherwise noted). The Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available online at www.morganstanley.com/im or by calling toll-free (800) 869-NEWS.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's Class A shares' performance from year-to-year and by showing how the Fund's average annual returns for the one, five and 10 year periods compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800) 869-NEWS
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.morganstanley.com/im
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns-Calendar Years*
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The performance information in the bar chart does not reflect the deduction of sales charges; if these amounts were reflected, returns would be less than shown.
Bar Chart Footnotes [Text Block] rr_BarChartFootnotesTextBlock

*  The Fund previously disclosed the total return of Class B shares. However, Class B shares are closed to new investments. The bar chart now shows Class A shares which remain open to new investments.

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

High Quarter

 

9/30/12

   

3.85

%

 

Low Quarter

 

3/31/08

   

–4.75

%

 
Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] rr_BarChartReasonSelectedClassDifferentFromImmediatelyPrecedingPeriod The Fund previously disclosed the total return of Class B shares. However, Class B shares are closed to new investments. The bar chart now shows Class A shares which remain open to new investments.
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel High Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.85%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Low Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (4.75%)
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads The Fund's returns in the table include the maximum applicable sales charge for each Class and assume you sold your shares at the end of each period (unless otherwise noted).
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the Fund's other Classes will vary from the Class A shares' returns.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes. After-tax returns for the Fund's other Classes will vary from the Class A shares' returns. Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For Periods Ended December 31, 2012
Barclays Capital Mortgage Index (reflects no deduction for fees, expenses or taxes)
 
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.59% [1]
5 Years rr_AverageAnnualReturnYear05 5.67% [1]
10 Years rr_AverageAnnualReturnYear10 5.08% [1]
Lipper U.S. Mortgage Funds Index (reflects no deduction for taxes)
 
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.60% [2]
5 Years rr_AverageAnnualReturnYear05 5.56% [2]
10 Years rr_AverageAnnualReturnYear10 4.60% [2]
Class A
 
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.25%
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther none [3]
Advisory Fee rr_ManagementFeesOverAssets 0.47%
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets 0.25% [4]
Other Expenses rr_OtherExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.28% [5]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.28%) [5]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 1.00% [5]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 523
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 730
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 954
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,598
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 523
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 730
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 954
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,598
Annual Return 2003 rr_AnnualReturn2003 1.84%
Annual Return 2004 rr_AnnualReturn2004 3.82%
Annual Return 2005 rr_AnnualReturn2005 2.31%
Annual Return 2006 rr_AnnualReturn2006 3.49%
Annual Return 2007 rr_AnnualReturn2007 5.20%
Annual Return 2008 rr_AnnualReturn2008 (8.64%)
Annual Return 2009 rr_AnnualReturn2009 7.05%
Annual Return 2010 rr_AnnualReturn2010 5.89%
Annual Return 2011 rr_AnnualReturn2011 5.71%
Annual Return 2012 rr_AnnualReturn2012 8.41%
1 Year rr_AverageAnnualReturnYear01 3.80%
5 Years rr_AverageAnnualReturnYear05 2.59%
10 Years rr_AverageAnnualReturnYear10 2.95%
Class A | After Taxes on Distributions
 
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.46% [6]
5 Years rr_AverageAnnualReturnYear05 1.29% [6]
10 Years rr_AverageAnnualReturnYear10 1.49% [6]
Class A | After Taxes on Distributions and Sales
 
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.45%
5 Years rr_AverageAnnualReturnYear05 1.42%
10 Years rr_AverageAnnualReturnYear10 1.63%
Class B
 
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther 5.00% [7]
Advisory Fee rr_ManagementFeesOverAssets 0.47%
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets 0.85% [4]
Other Expenses rr_OtherExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.88% [5]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.28%) [5]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 1.60% [5]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock The Class B CDSC is scaled down to 1.00% during the sixth year, reaching zero thereafter. See "Share Class Arrangements" for a complete discussion of the CDSC.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 663
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 805
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,071
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,740
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 163
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 505
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 871
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,740
1 Year rr_AverageAnnualReturnYear01 2.91%
5 Years rr_AverageAnnualReturnYear05 2.53%
10 Years rr_AverageAnnualReturnYear10 2.88% [8]
Class L
 
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [9]
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther none [9]
Advisory Fee rr_ManagementFeesOverAssets 0.47% [9]
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets 0.50% [4],[9]
Other Expenses rr_OtherExpensesOverAssets 0.56% [9]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.53% [5],[9]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.28%) [5],[9]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 1.25% [5],[9]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 127 [9]
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 397 [9]
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 686 [9]
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,511 [9]
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 127 [9]
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 397 [9]
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 686 [9]
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,511 [9]
1 Year rr_AverageAnnualReturnYear01 6.91% [10]
5 Years rr_AverageAnnualReturnYear05 2.91% [10]
10 Years rr_AverageAnnualReturnYear10 2.78% [10]
Class I
 
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value at redemption) rr_MaximumDeferredSalesChargeOverOther none
Advisory Fee rr_ManagementFeesOverAssets 0.47%
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets none [4]
Other Expenses rr_OtherExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.03% [5]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.28%) [5]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.75% [5]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 77
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 240
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 417
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 930
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 77
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 240
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 417
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 930
1 Year rr_AverageAnnualReturnYear01 8.74%
5 Years rr_AverageAnnualReturnYear05 3.78%
10 Years rr_AverageAnnualReturnYear10 3.66%
[1] The Barclays Capital Mortgage Index covers the mortgage-backed pass-through securities of Ginnie Mae (GNMA), Fannie Mae (FNMA), and Freddie Mac (FHLMC). This Index is the Mortgage Backed Securities Fixed Rate component of the Barclays Capital U.S. Aggregate Index. It is not possible to invest directly in an index.
[2] The Lipper U.S. Mortgage Funds Index is an equally weighted performance index of the largest qualifying funds (based on net assets) in the Lipper U.S. Mortgage Funds classification. There are currently 30 funds represented in this Index.
[3] Investments that are not subject to any sales charges at the time of purchase are subject to a contingent deferred sales charge ("CDSC") of 1.00% that will be imposed if you sell your shares within 18 months after purchase, except for certain specific circumstances.
[4] The Board of Trustees approved an amendment to the Plan of Distribution reducing the distribution and shareholder services (12b-1) fee for the Fund's Class L shares from 0.85% to 0.50% of the average daily net assets of such Class, effective February 25, 2013. The Distribution and/or Shareholder Service (12b-1) Fee shown in the table above has been restated to reflect such change.
[5] The Fund's "Adviser," Morgan Stanley Investment Management Inc., and its "Administrator," Morgan Stanley Services Company Inc., have agreed to reduce its advisory fee, its administration fee and/or reimburse the Fund so that Total Annual Fund Operating Expenses, excluding brokerage fees and 12b-1 fees, will not exceed 0.75% for each Class. The fee waivers and/or expense reimbursements will continue for at least one year or until such time as the Fund's Board of Trustees acts to discontinue all or a portion of such waivers and/or reimbursements when it deems such action is appropriate.
[6] These returns do not reflect any tax consequences from a sale of your shares at the end of each period.
[7] The Class B CDSC is scaled down to 1.00% during the sixth year, reaching zero thereafter. See "Share Class Arrangements" for a complete discussion of the CDSC.
[8] Effective April 2005, Class B shares will generally convert to Class A shares approximately eight years after the end of the calendar month in which the shares were purchased. The "Past 10 Years" performance for Class B shares reflects this conversion.
[9] Effective February 25, 2013, Class C shares were renamed Class L shares.
[10] Effective February 25, 2013, Class C shares were renamed Class L shares. The one year performance of Class L shares reflects the 1% contingent deferred sales charge (CDSC) in effect for Class C shares as of December 31, 2012. Class C shares held for less than one year were subject to a 1% CDSC. The CDSC on Class L shares was eliminated effective February 25, 2013.
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