<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>10801 - Disclosure - Senior Unsecured Notes</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2010 - 12/31/2010
USD ($)

USD ($) / shares

</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>Duration_1_1_2010_To_12_31_2010</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001067063</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2010-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2010-12-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><UnitID>Unit1</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Unit13</UnitID><UnitType>Divide</UnitType><NumeratorMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></NumeratorMeasure><DenominatorMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></DenominatorMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Unit12</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="12 Months Ended" /><Label Id="2" Label="Dec. 31, 2010" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>clip_SeniorUnsecuredNotesAbstract</ElementName><ElementPrefix>clip</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>SENIOR UNSECURED NOTES [Abstract]</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>SENIOR UNSECURED NOTES [Abstract]</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Senior Unsecured Notes</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>clip_SeniorUnsecuredNotesTextBlock</ElementName><ElementPrefix>clip</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>SENIOR UNSECURED NOTES [Text Block]</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div&gt;

&lt;div&gt;

&lt;div&gt;

&lt;table style="font-family: Times New Roman; font-size: 10pt;" cellspacing="0" cellpadding="0" width="100%"&gt;
&lt;tr valign="top"&gt;&lt;td style="width: 18pt;" align="right"&gt;

&lt;div&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt; font-weight: bold;" class="_mt"&gt;8.&amp;nbsp;&amp;nbsp;&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td&gt;

&lt;div style="text-indent: 0pt; margin-left: 0pt; margin-right: 0pt;" align="justify"&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt; font-weight: bold;" class="_mt"&gt;&lt;font style="display: inline; text-decoration: underline;" class="_mt"&gt;SENIOR UNSECURED NOTES&lt;/font&gt;&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block;"&gt;&lt;br /&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="justify"&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt;" class="_mt"&gt;A summary of the Company's senior unsecured notes as of December 31, 2010 and 2009 is as follows:&amp;nbsp;&amp;nbsp;&lt;font style="font-style: italic; display: inline;" class="_mt"&gt;(dollars in thousands)&lt;/font&gt;&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block;"&gt;&lt;br /&gt;&lt;/div&gt;

&lt;div&gt;

&lt;table style="font-family: Times New Roman; font-size: 10pt;" cellspacing="0" cellpadding="0" width="100%"&gt;
&lt;tr&gt;&lt;td valign="top" width="43%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 2.1pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;December 31,&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="12%" align="right"&gt;

&lt;div&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;December 31,&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Effective&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td style="border-bottom: black 2px solid;" valign="top" width="43%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 2.1pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2010&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="12%" align="right"&gt;

&lt;div&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2009&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Rate (1)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.050% Senior Unsecured Notes, due April 15, 2010 (2)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;--&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&lt;font style="margin-left: 12.6pt;" class="_mt"&gt; &lt;/font&gt;$149,984&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.265%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;7.835% Senior Unsecured Notes, due December 15, 2010 (2)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;--&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="12%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 2.1pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;15,000&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;7.950%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;7.750% Senior Unsecured Notes, due February 15, 2011 (3)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;--&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;299,814&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;7.930%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.250% Senior Unsecured Notes, due January 15, 2012&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;$&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;99,793&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;99,599&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.457%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;6.150% Senior Unsecured Notes, due December 15, 2012&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;93,946&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;93,455&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;6.894%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.820% Senior Unsecured Notes, due March 15, 2013&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;25,861&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;25,751&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;6.448%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;4.600% Senior Unsecured Notes, due June 15, 2013&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;99,930&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;99,901&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;4.742%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.125% Senior Unsecured Notes, due February 15, 2014&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;200,749&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;200,989&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.110%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.125% Senior Unsecured Notes, due January 15, 2015&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;149,625&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;149,533&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.297%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.800% Senior Unsecured Notes, due January 15, 2016&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;200,389&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;200,464&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;5.806%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td style="border-bottom: black 2px solid;" valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;7.750% Senior Unsecured Notes, due August 15, 2019&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;248,158&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid; text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;247,944&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="11%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 3.6pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;8.017%&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="13%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="12%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="11%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td style="border-bottom: black 3px double;" valign="top" width="43%" align="left"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Total Senior Unsecured Notes&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 3px double;" valign="top" width="13%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 2.1pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;$1,118,451&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 3px double; text-align: right;" valign="top" width="12%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;$1,582,434&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 3px double;" valign="top" width="11%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="43%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="13%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="12%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="11%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="79%" colspan="4" align="left"&gt;

&lt;div style="text-indent: -18pt; display: block; margin-left: 18pt; margin-right: 3.6pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;(1)&amp;nbsp;&amp;nbsp;&amp;nbsp;Includes the cost of terminated treasury lock agreements (if any), offering and other transaction costs and the discount/premium on the notes, as applicable.&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="79%" colspan="4" align="left"&gt;

&lt;div style="text-indent: -18pt; display: block; margin-left: 18pt; margin-right: 3.6pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;(2)&amp;nbsp;&amp;nbsp; These notes were paid at maturity.&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="79%" colspan="4" align="left"&gt;

&lt;div style="text-indent: -18pt; display: block; margin-left: 18pt; margin-right: 3.6pt;" align="left"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;(3)&amp;nbsp;&amp;nbsp; On December 15, 2010, the Company redeemed $300 million principal amount of its 7.75 percent senior unsecured notes due February 15, 2011.&amp;nbsp; The redemption price, including a make-whole premium, was 101.225 percent of the principal amount of the notes, plus accrued and unpaid interest up to the redemption date. &amp;nbsp;The Company funded the redemption price, including accrued and unpaid interest, of approximately $311.4 million from borrowing on its unsecured revolving credit facility, as well as cash on hand. &amp;nbsp;In connection with the redemption, the Company recorded approximately $3.8 million as a loss from early extinguishment of debt.&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;&lt;/div&gt; &lt;/div&gt;</NonNumbericText><NonNumericTextHeader>8.&amp;nbsp;&amp;nbsp;


SENIOR UNSECURED NOTES



A summary of the Company's senior unsecured notes as of December 31, 2010 and 2009 is as</NonNumericTextHeader><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>us-types:textBlockItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>SENIOR UNSECURED NOTES [Text Block]</ElementDefenition><ElementReferences>No authoritative reference available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Senior Unsecured Notes</Label></Row></Rows><Footnotes /><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows><ReportName>Senior Unsecured Notes</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>false</HasCustomUnits><SharesShouldBeRounded>true</SharesShouldBeRounded></InstanceReport>
