Pooled Trust Preferred Securities that have at Least One Credit Rating Below Investment Grade (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2011 Entity
INCAPS Funding I
Schedule of Investments [Line Items]
Book value	$ 14,964
Fair value	17,828
Unrealized gain (loss)	2,864
Lowest credit rating assigned to security	CCC-
Number of banks/insurance companies currently performing	24
Actual deferrals and defaults as a percentage of original collateral	11.00%
Expected deferrals and defaults as a percentage of remaining performing collateral	20.00%
Excess subordination as a percentage of remaining performing collateral	27.00%
Alesco Preferred Funding VII Ltd
Schedule of Investments [Line Items]
Book value	553
Fair value	374
Unrealized gain (loss)	(179)
Lowest credit rating assigned to security	C
Number of banks/insurance companies currently performing	61
Actual deferrals and defaults as a percentage of original collateral	30.00%
Expected deferrals and defaults as a percentage of remaining performing collateral	26.00%
Preferred Term Securities II
Schedule of Investments [Line Items]
Book value	627
Fair value	904
Unrealized gain (loss)	$ 277
Lowest credit rating assigned to security	C
Number of banks/insurance companies currently performing	24
Actual deferrals and defaults as a percentage of original collateral	36.00%
Expected deferrals and defaults as a percentage of remaining performing collateral	19.00%
Expected recoveries as a percentage of remaining performing collateral	2.00%

Number of banks currently performing

Name:	nyb_NumberOfBanksCurrentlyPerforming
Namespace Prefix:	nyb
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of Actual deferrals and defaults to original collateral

+ Details

Name:	nyb_PercentageOfActualDeferralsAndDefaultsToOriginalCollateral
Namespace Prefix:	nyb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of excess subordination to remaining performing collateral

+ Details

Name:	nyb_PercentageOfExcessSubordinationToRemainingPerformingCollateral
Namespace Prefix:	nyb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of expected deferrals and defaults to remaining performing collateral

+ Details

Name:	nyb_PercentageOfExpectedDeferralsAndDefaultsToRemainingPerformingCollateral
Namespace Prefix:	nyb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of expected recoveries to remaining performing collateral

+ Details

Name:	nyb_PercentageOfExpectedRecoveriesToRemainingPerformingCollateral
Namespace Prefix:	nyb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Securities, Gross Unrealized Gain (Loss)

+ Details

Name:	nyb_SecuritiesGrossUnrealizedGainLoss
Namespace Prefix:	nyb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Trust Preferred Securities Carrying Value

+ Details

Name:	nyb_TrustPreferredSecuritiesCarryingValue
Namespace Prefix:	nyb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Trust Preferred Securities Fair Value

+ Details

Name:	nyb_TrustPreferredSecuritiesFairValue
Namespace Prefix:	nyb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Description of the credit rating indicative of likelihood of repayment of the debt instrument given by a credit rating agency (for example, Standard and Poor's, Moody's, Fitch).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 129
-Paragraph 2, 4
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

+ Details

Name:	us-gaap_DebtInstrumentCreditRating
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_ScheduleOfInvestmentsLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration