Loans and Leases Receivable and Allowance for Credit Losses - Schedule of Loans and Leases Receivable (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, mortgage warehouse, at fair value			$ 2,245,758
Loans and leases receivable	$ 7,353,262		7,318,988
Allowance for credit losses on loans and leases	(149,283)	$ (136,200)	(56,379)	$ (43,679)	$ (39,972)
Total loans and leases receivable, net of allowance for credit losses	9,721,991		9,508,367
Deferred (fees) costs and unamortized (discounts) premiums, net	(3,200)		(2,100)
Mortgage Warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, mortgage warehouse, at fair value	2,518,012		2,245,758
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	1,621,633		1,909,274
Allowance for credit losses on loans and leases	(8,750)		(6,157)	(10,630)	(11,462)
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	115,448		118,418
Allowance for credit losses on loans and leases	(1,934)		(1,262)	(584)	(624)
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	362,047		375,014
Allowance for credit losses on loans and leases	(4,180)		(3,218)	(6,572)	(3,654)
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	69,240		70,398
Allowance for credit losses on loans and leases	(4,987)		(1,060)	(117)	(145)
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	1,315,171		1,178,283
Allowance for credit losses on loans and leases	(83,569)		(20,648)	$ (3,689)	$ (2,529)
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	5,606,804		5,690,820
Commercial | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	1,621,633		1,907,331
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	2,072,952		1,891,152
Commercial | Commercial real estate owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	543,945		551,948
Commercial | Commercial real estate non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	1,252,826		1,222,772
Commercial | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	115,448		117,617
Commercial | Direct Finance Equipment Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	96,600		89,200
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	1,746,458		1,628,168
Consumer | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	362,047		382,634
Consumer | Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	69,240		71,359
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable	$ 1,315,171		$ 1,174,175