Loan Portfolio by Credit Quality Indicator (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		$ 39,418,757	$ 38,359,022
Multi-Family
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		29,211,541	28,074,709
Multi-Family | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		29,019,539	27,874,330
Multi-Family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		172,517	125,752
Multi-Family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		19,485	74,627
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		7,153,868	7,322,226
Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		7,101,257	7,255,100
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		46,973	47,123
Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		5,638	20,003
One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		449,419	477,228
One-to-four family | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		444,093	471,571
One-to-four family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		3,657	3,691
One-to-four family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		1,669	1,966
Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		424,827	435,825
Acquisition, Development and Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		341,154	344,040
Acquisition, Development and Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		74,121	76,033
Acquisition, Development and Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		9,552	15,752
Mortgage Receivable
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		37,239,655	36,309,988
Mortgage Receivable | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		36,906,043	35,945,041
Mortgage Receivable | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		297,268	252,599
Mortgage Receivable | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		36,344	112,348
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	2,170,439	2,040,574
Commercial and Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	2,080,569	1,925,527
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	16,302	20,883
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans	[1]	73,568	94,164
Other
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		8,663	8,460
Other | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		8,659	8,449
Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		4	11
Total Other Loans
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		2,179,102	2,049,034
Total Other Loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		2,089,228	1,933,976
Total Other Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		16,302	20,883
Total Other Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Non-Covered Loans		$ 73,572	$ 94,175

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