Loans Receivable and Allowance for Loan Losses - Schedule of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	$ 37,605	$ 33,566	$ 35,647	$ 30,932
Charge-offs	(1,140)	(1,804)	(1,182)	(2,948)
Recoveries	80	805	577	948
Provision for loan losses	1,552	4,924	3,055	8,559
Ending balance as of June 30,	38,097	37,491	38,097	37,491
Loans:
Individually evaluated for impairment					$ 57,916	$ 44,608
Collectively evaluated for impairment					6,017,041	5,366,057
Loans receivable, gross					6,114,274	5,453,145
Allowance for loan losses:
Individually evaluated for impairment					3,666	2,273
Collectively evaluated for impairment					29,100	27,212
Total Allowance for loan losses	37,605	33,566	35,647	30,932	38,097	35,647
Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					39,317	42,480
Allowance for loan losses:
Loans acquired with credit deterioration					5,331	6,162
Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	12,135	8,196	12,016	8,493
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	233	538	352	241
Ending balance as of June 30,	12,368	8,734	12,368	8,734
Loans:
Individually evaluated for impairment					386	661
Collectively evaluated for impairment					3,304,609	2,905,128
Loans receivable, gross					3,308,556	2,909,439
Allowance for loan losses:
Individually evaluated for impairment					202	0
Collectively evaluated for impairment					12,166	12,016
Total Allowance for loan losses	12,135	8,196	12,016	8,493	12,368	12,016
Multi-family | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					3,561	3,650
Allowance for loan losses:
Loans acquired with credit deterioration					0	0
Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	9,959	6,747	8,864	4,784
Charge-offs	(537)	(1,213)	(537)	(1,234)
Recoveries	55	58	111	103
Provision for loan losses	893	8,470	1,932	10,409
Ending balance as of June 30,	10,370	14,062	10,370	14,062
Loans:
Individually evaluated for impairment					28,564	17,621
Collectively evaluated for impairment					814,372	783,986
Loans receivable, gross					843,868	803,159
Allowance for loan losses:
Individually evaluated for impairment					3,183	1,990
Collectively evaluated for impairment					6,968	6,650
Total Allowance for loan losses	9,959	6,747	8,864	4,784	10,370	8,864
Commercial and industrial | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					932	1,552
Allowance for loan losses:
Loans acquired with credit deterioration					219	224
Commercial real estate - owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	1,410	4,583	1,348	4,336
Charge-offs	0	(270)	0	(343)
Recoveries	0	1	0	1
Provision for loan losses	172	(663)	234	(343)
Ending balance as of June 30,	1,582	3,651	1,582	3,651
Loans:
Individually evaluated for impairment					9,840	8,329
Collectively evaluated for impairment					326,446	286,951
Loans receivable, gross					348,806	308,241
Allowance for loan losses:
Individually evaluated for impairment					0	1
Collectively evaluated for impairment					1,582	1,347
Total Allowance for loan losses	1,410	4,583	1,348	4,336	1,582	1,348
Commercial real estate - owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					12,520	12,961
Allowance for loan losses:
Loans acquired with credit deterioration					0	0
Commercial real estate - non-owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	8,548	9,738	8,420	9,198
Charge-offs	0	0	0	(245)
Recoveries	0	0	8	0
Provision for loan losses	(65)	(3,428)	55	(2,643)
Ending balance as of June 30,	8,483	6,310	8,483	6,310
Loans:
Individually evaluated for impairment					5,962	4,831
Collectively evaluated for impairment					1,122,972	939,368
Loans receivable, gross					1,139,711	956,255
Allowance for loan losses:
Individually evaluated for impairment					177	148
Collectively evaluated for impairment					4,535	3,858
Total Allowance for loan losses	8,548	9,738	8,420	9,198	8,483	8,420
Commercial real estate - non-owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					10,777	12,056
Allowance for loan losses:
Loans acquired with credit deterioration					3,771	4,414
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	1,264	852	1,074	1,047
Charge-offs	0	(295)	0	(1,064)
Recoveries	24	172	457	187
Provision for loan losses	(79)	115	(322)	674
Ending balance as of June 30,	1,209	844	1,209	844
Loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					99,381	87,006
Loans receivable, gross					99,615	87,240
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					1,209	1,074
Total Allowance for loan losses	1,264	852	1,074	1,047	1,209	1,074
Construction | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					234	234
Allowance for loan losses:
Loans acquired with credit deterioration					0	0
Residential real estate
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	3,676	2,995	3,298	2,698
Charge-offs	(413)	(26)	(413)	(26)
Recoveries	1	572	1	572
Provision for loan losses	271	(86)	649	211
Ending balance as of June 30,	3,535	3,455	3,535	3,455
Loans:
Individually evaluated for impairment					4,270	4,726
Collectively evaluated for impairment					250,466	258,446
Loans receivable, gross					262,567	271,613
Allowance for loan losses:
Individually evaluated for impairment					104	84
Collectively evaluated for impairment					2,491	2,141
Total Allowance for loan losses	3,676	2,995	3,298	2,698	3,535	3,298
Residential real estate | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					7,831	8,441
Allowance for loan losses:
Loans acquired with credit deterioration					940	1,073
Manufactured housing
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	468	346	494	262
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	(28)	(30)	(54)	54
Ending balance as of June 30,	440	316	440	316
Loans:
Individually evaluated for impairment					8,850	8,300
Collectively evaluated for impairment					95,788	101,838
Loans receivable, gross					107,874	113,490
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					96	98
Total Allowance for loan losses	468	346	494	262	440	494
Manufactured housing | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					3,236	3,352
Allowance for loan losses:
Loans acquired with credit deterioration					344	396
Other
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of March 31,	145	109	133	114
Charge-offs	(190)	0	(232)	(36)
Recoveries	0	2	0	85
Provision for loan losses	155	8	209	(44)
Ending balance as of June 30,	110	119	110	119
Loans:
Individually evaluated for impairment					44	140
Collectively evaluated for impairment					3,007	3,334
Loans receivable, gross					3,277	3,708
Allowance for loan losses:
Individually evaluated for impairment					0	50
Collectively evaluated for impairment					53	28
Total Allowance for loan losses	$ 145	$ 109	$ 133	$ 114	110	133
Other | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					226	234
Allowance for loan losses:
Loans acquired with credit deterioration					$ 57	$ 55