Composition of Loan and Lease Portfolio (Detail) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018		Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 40,833,446	$ 40,133,861
Net deferred loan origination costs		43,255	32,047
Allowance for losses		(151,112)	(159,820)		$ (160,652)	$ (158,046)
Total loans and leases, net		$ 40,725,589	$ 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]	$ 2,776,819	$ 2,388,420	[2]
Non-Covered Loans, Percentage	[1]	6.80%	5.95%
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,767,472	$ 1,705,308
Non-Covered Loans, Percentage		4.33%	4.25%
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 30,465,835	$ 29,883,919
Non-Covered Loans, Percentage		74.61%	74.46%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,898,577	$ 6,998,834
Non-Covered Loans, Percentage		16.89%	17.44%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 417,605	$ 446,094
Non-Covered Loans, Percentage		1.03%	1.11%
Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 266,282	$ 407,870
Non-Covered Loans, Percentage		0.65%	1.02%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 38,048,299	$ 37,736,717
Allowance for losses		$ (122,088)	$ (130,983)		$ (129,697)	$ (128,275)
Non-Covered Loans, Percentage		93.18%	94.03%
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,009,347	$ 683,112
Non-Covered Loans, Percentage		2.47%	1.70%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 8,328	$ 8,724
Non-Covered Loans, Percentage		0.02%	0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,785,147	$ 2,397,144
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 2,785,147	$ 2,397,144
Non-Covered Loans, Percentage		6.82%	5.97%

[1] Includes specialty finance loans and leases of $2.3 billion and $1.9 billion, respectively, at June 30, 2019 and December 31, 2018. Other C&I loans of $456.1 million and $469.9 million, respectively, at June 30, 2019 and December 31, 2018.

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