Composition of Loan and Lease Portfolio (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 40,798,440	$ 40,133,861
Net deferred loan origination costs		45,780	32,047
Allowance for losses		(149,433)	(159,820)	$ (159,655)	$ (158,046)
Total loans and leases, net		$ 40,694,787	$ 40,006,088
Non-Covered Loans, Percentage		100.00%	100.00%
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[1],[2]	$ 2,842,152	$ 2,388,420
Non-Covered Loans, Percentage	[2]	6.97%	5.95%
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,784,081	$ 1,705,308
Non-Covered Loans, Percentage		4.37%	4.25%
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 30,269,409	$ 29,883,919
Non-Covered Loans, Percentage		74.19%	74.46%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,985,568	$ 6,998,834
Non-Covered Loans, Percentage		17.12%	17.44%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 395,044	$ 446,094
Non-Covered Loans, Percentage		0.97%	1.11%
Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 297,526	$ 407,870
Non-Covered Loans, Percentage		0.73%	1.02%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 37,947,547	$ 37,736,717
Allowance for losses		$ (122,967)	$ (130,983)	$ (128,816)	$ (128,275)
Non-Covered Loans, Percentage		93.01%	94.03%
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,058,071	$ 683,112
Non-Covered Loans, Percentage		2.60%	1.70%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 8,741	$ 8,724
Non-Covered Loans, Percentage		0.02%	0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,850,893	$ 2,397,144
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,850,893	$ 2,397,144
Non-Covered Loans, Percentage		6.99%	5.97%

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

[2] Includes specialty finance loans and leases of $2.4 billion and $1.9 billion, respectively, at September 30, 2019 and December 31, 2018. Other C&I loans of $447.1 million and $469.9 million, respectively, at September 30, 2019 and December 31, 2018.