Loans and Leases - Composition of Loan and Lease Portfolio (Detail) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 42,235,977	$ 41,844,019
Net deferred loan origination costs		55,782	50,136
Allowance for loan and lease losses		(162,244)	(147,638)	$ (156,636)	$ (159,820)
Total loans and leases, net		$ 42,129,515	$ 41,746,517
Non-Covered Loans, Percentage		100.00%	100.00%
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[1],[2]	$ 3,437,694	$ 3,014,378
Non-Covered Loans, Percentage	[2]	8.14%	7.20%
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,953,431	$ 1,742,380
Non-Covered Loans, Percentage		4.62%	4.16%
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 31,271,073	$ 31,158,672
Non-Covered Loans, Percentage		74.04%	74.46%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 7,034,720	$ 7,081,910
Non-Covered Loans, Percentage		16.67%	16.93%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 352,301	$ 380,361
Non-Covered Loans, Percentage		0.83%	0.91%
Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 130,675	$ 200,596
Non-Covered Loans, Percentage		0.30%	0.48%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[3]	$ 38,788,769	$ 38,821,539
Allowance for loan and lease losses		$ (141,314)	$ (122,695)	$ (128,766)	$ (130,983)
Non-Covered Loans, Percentage	[3]	91.84%	92.78%
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,484,263	$ 1,271,998
Non-Covered Loans, Percentage		3.52%	3.04%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 9,514	$ 8,102
Non-Covered Loans, Percentage		0.02%	0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 3,447,208	$ 3,022,480
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[3]	$ 3,447,208	$ 3,022,480
Non-Covered Loans, Percentage	[3]	8.16%	7.22%

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

[2] Includes specialty finance loans and leases of $3.0 billion and $2.6 billion, respectively, at March 31, 2020 and December 31, 2019, and other C&I loans of $432.8 million and $420.1 million, respectively, at March 31, 2020 and December 31, 2019.

[3] Excludes accrued interest receivable of $119.6 million and $116.9 million at March 31, 2020 and December 31, 2019, respectively, that is included in other assets in the Consolidated Statements of Condition.