Loans Receivable and Allowance for Loan Losses - Schedule of Loans Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 FDIC	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	$ 4,299,738	$ 4,269,480
Total loans receivable covered under FDIC loss sharing agreements	37,365	42,181
Total loans receivable	4,337,103	4,311,661
Deferred (fees) costs and unamortized premiums/(discounts), net	748	512
Allowance for loan losses	(33,566)	(30,932)	(26,704)	(23,998)
Total loans receivable, net of allowance for loan losses	4,304,285	4,281,241
Loans acquired in FDIC-assisted transactions	2
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	2,053,740	2,127,406
Allowance for loan losses	(8,196)	(8,493)	(6,220)	(4,227)
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	1,194,072	1,149,657
Allowance for loan losses	(14,321)	(13,572)	(12,632)	(11,478)
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	607,837	542,665
Allowance for loan losses	(6,747)	(4,746)	(2,483)	(2,674)
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	66,405	63,374
Allowance for loan losses	(852)	(1,047)	(2,342)	(2,385)
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	289,326	297,395
Allowance for loan losses	(2,995)	(2,698)	(2,307)	(2,490)
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	121,622	126,731
Allowance for loan losses	(346)	(262)	(593)	(614)
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable	4,101	4,433
Allowance for loan losses	(109)	(114)	(127)	(130)
Commercial Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	3,899,625	3,856,205
Total loans receivable covered under FDIC loss sharing agreements	22,429	26,897
Commercial Loan | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	2,053,379	2,127,034
Total loans receivable covered under FDIC loss sharing agreements	361	372
Commercial Loan | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	1,177,725	1,132,072
Total loans receivable covered under FDIC loss sharing agreements	16,347	17,585
Commercial Loan | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	606,091	540,430
Total loans receivable covered under FDIC loss sharing agreements	1,746	2,235
Commercial Loan | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	62,430	56,669
Total loans receivable covered under FDIC loss sharing agreements	3,975	6,705
Consumer Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	400,113	413,275
Total loans receivable covered under FDIC loss sharing agreements	14,936	15,284
Consumer Loan | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	277,167	285,003
Total loans receivable covered under FDIC loss sharing agreements	12,159	12,392
Consumer Loan | Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	121,622	126,731
Consumer Loan | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable not covered under FDIC loss sharing agreements	1,324	1,541
Total loans receivable covered under FDIC loss sharing agreements	$ 2,777	$ 2,892