Non-Covered Loan Portfolio by Credit Quality Indicator (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		$ 34,124,905	$ 33,004,361
Multi-Family
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		24,635,567	23,831,846
Multi-Family | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		24,597,041	23,777,569
Multi-Family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		6,322	6,798
Multi-Family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		32,204	47,479
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		7,642,994	7,634,320
Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		7,618,479	7,591,223
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		3,327	9,123
Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		21,188	33,974
One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		102,317	138,915
One-to-four family | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		90,872	127,883
One-to-four family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		11,445	11,032
Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		294,768	258,116
Acquisition, Development and Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		293,492	256,868
Acquisition, Development and Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,276	1,248
Mortgage Receivable
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		32,675,646	31,863,197
Mortgage Receivable | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		32,599,884	31,753,543
Mortgage Receivable | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		9,649	15,921
Mortgage Receivable | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		66,113	93,733
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	1,410,214	1,109,221	[2]
Commercial and Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	1,390,799	1,083,173
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	14,050	17,032
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	5,365	9,016
Other
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		26,069	31,943
Other | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		24,576	30,974
Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,493	969
Total Other Loan Segment
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,436,283	1,141,164
Total Other Loan Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,415,375	1,114,147
Total Other Loan Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		14,050	17,032
Total Other Loan Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		$ 6,858	$ 9,985

[1] Includes lease financing receivables, all of which were classified as "pass."

[2] Includes lease financing receivables, all of which were current.