Composition of Loan Portfolio (Detail) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 40,133,861	$ 38,359,022
Net deferred loan origination costs		32,047	28,949
Allowance for losses		(159,820)	(158,046)	$ (158,290)
Loans held for investment, net		40,006,088	38,229,925
Loans held for sale			35,258
Total loans, net		$ 40,006,088	$ 38,265,183
Non-Covered Loans, Percentage		100.00%	100.00%
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[1]	$ 2,388,420	$ 2,040,574
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,705,308	$ 1,377,964
Non-Covered Loans, Percentage		4.25%	3.59%
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 29,883,919	$ 28,074,709
Non-Covered Loans, Percentage		74.46%	73.19%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,998,834	$ 7,322,226
Non-Covered Loans, Percentage		17.44%	19.09%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 446,094	$ 477,228
Non-Covered Loans, Percentage		1.11%	1.24%
Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 407,870	$ 435,825
Non-Covered Loans, Percentage		1.02%	1.14%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 37,736,717	$ 36,309,988
Allowance for losses		$ (130,983)	$ (128,275)	$ (125,416)
Non-Covered Loans, Percentage		94.03%	94.66%
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 683,112	$ 662,610
Non-Covered Loans, Percentage		1.70%	1.73%
Other Commercial and Industrial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 2,388,420	$ 2,040,574
Non-Covered Loans, Percentage	[2]	5.95%	5.32%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 8,724	$ 8,460
Non-Covered Loans, Percentage		0.02%	0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,397,144	$ 2,049,034
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,397,144	$ 2,049,034
Non-Covered Loans, Percentage		5.97%	5.34%

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

[2] Includes specialty finance loans and leases of $1.9 billion and $1.5 billion, respectively, at December 31, 2018 and 2017. Other C&I loans of $469.9 million and $500.8 million, respectively, at December 31, 2018 and 2017.