Loans Receivable and Allowance for Loan Losses - Schedule of Loans Receivable (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 FDIC	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	$ 4,269,480	$ 2,399,265
Total loan receivable covered under FDIC loss sharing agreements	42,181	66,725
Total all loans	4,311,661	2,465,990
Deferred (fees) costs and unamortized premiums/(discounts), net	512	(912)
Allowance for loan losses	(30,932)	(23,998)	(25,837)	(15,032)
Total loans receivable, net of allowance for loan losses	4,281,241	2,441,080
Loans acquired in FDIC-assisted transactions	2
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	2,127,406	1,064,058
Allowance for loan losses	(8,493)	(4,227)	(1,795)
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	1,149,657	753,591
Allowance for loan losses	(13,572)	(11,478)	(13,644)
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	542,665	296,595
Allowance for loan losses	(4,746)	(2,674)	(1,548)
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	63,374	42,917
Allowance for loan losses	(1,047)	(2,385)	(3,991)
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	297,395	163,921
Allowance for loan losses	(2,698)	(2,490)	(3,233)
Manufactured Housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	126,731	139,471
Allowance for loan losses	(262)	(614)	(750)
Home equity / other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total all loans	4,433	5,437
Allowance for loan losses	(114)	(130)	(154)
Commercial Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	3,856,205	2,112,462
Total loan receivable covered under FDIC loss sharing agreements	26,897	44,700
Commercial Loan | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	2,127,034	1,063,459
Total loan receivable covered under FDIC loss sharing agreements	372	600
Commercial Loan | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,132,072	724,752
Total loan receivable covered under FDIC loss sharing agreements	17,585	28,839
Commercial Loan | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	540,430	292,937
Total loan receivable covered under FDIC loss sharing agreements	2,235	3,658
Commercial Loan | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	56,669	31,314
Total loan receivable covered under FDIC loss sharing agreements	6,705	11,603
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	413,275	286,803
Total loan receivable covered under FDIC loss sharing agreements	15,284	22,025
Consumer | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	285,003	145,188
Total loan receivable covered under FDIC loss sharing agreements	12,392	18,732
Consumer | Manufactured Housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	126,731	139,471
Consumer | Home equity / other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,541	2,144
Total loan receivable covered under FDIC loss sharing agreements	$ 2,892	$ 3,293