Composition of Loan Portfolio (Detail) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 37,335,541	$ 35,740,489
Net deferred loan origination costs		25,199	22,715
Allowance for losses on non-covered loans		(154,705)	(147,124)	$ (146,045)	$ (139,857)
Non-covered loans held for investment, net		37,206,035	35,616,080
Covered loans		1,789,164	2,060,089
Allowance for losses on covered loans		(25,360)	(31,395)	(37,632)	(45,481)
Covered loans, net		1,763,804	2,028,694
Loans held for sale		701,398	367,221
Total loans, net		$ 39,671,237	$ 38,011,995
Non-Covered Loans, Percentage		100.00%	100.00%
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 27,066,459	$ 25,971,629
Non-Covered Loans, Percentage		72.49%	72.67%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 7,764,241	$ 7,857,204
Non-Covered Loans, Percentage		20.80%	21.98%
Acquisition, Development and Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 372,199	$ 311,676
Non-Covered Loans, Percentage		1.00%	0.87%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 331,617	$ 116,841
Covered loans		$ 1,688,148
Non-Covered Loans, Percentage		0.89%	0.33%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 35,534,516	$ 34,257,350
Allowance for losses on non-covered loans		$ (126,234)	$ (124,478)	$ (121,568)	$ (122,616)
Non-Covered Loans, Percentage		95.18%	95.85%
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[1]	$ 1,775,295	$ 1,450,556
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,301,814	$ 1,085,529
Non-Covered Loans, Percentage		3.48%	3.04%
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 473,481	$ 365,027
Non-Covered Loans, Percentage		1.27%	1.02%
Other Commercial and Industrial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 1,775,295	$ 1,450,556
Non-Covered Loans, Percentage	[2]	4.75%	4.06%
Purchased Credit-Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 5,939	$ 8,344
Non-Covered Loans, Percentage		0.02%	0.02%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 19,791	$ 24,239
Non-Covered Loans, Percentage		0.05%	0.07%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,795,086	$ 1,474,795
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,801,025	$ 1,483,139
Non-Covered Loans, Percentage		4.82%	4.15%

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

[2] Includes specialty finance loans of $1.1 billion and $880.7 million, and other C&I loans of $630.7 million and $569.9 million, respectively, at September 30, 2016 and December 31, 2015.