Loans Receivable and Allowance for Loan Losses - Schedule of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	$ 38,097	$ 37,491	$ 35,647	$ 30,932
Charge-offs	(666)	(5,932)	(1,848)	(8,880)
Recoveries	378	275	955	1,223
Provision for loan losses	88	1,989	3,143	10,548
Ending balance as of September 30,	37,897	33,823	37,897	33,823
Loans:
Individually evaluated for impairment					$ 69,127	$ 44,608
Collectively evaluated for impairment					5,912,698	5,366,057
Loans receivable, gross					6,016,899	5,453,145
Allowance for loan losses:
Individually evaluated for impairment					3,404	2,273
Collectively evaluated for impairment					29,403	27,212
Total Allowance for loan losses	38,097	37,491	35,647	30,932	37,897	35,647
Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					35,074	42,480
Allowance for loan losses:
Loans acquired with credit deterioration					5,090	6,162
Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	12,368	8,734	12,016	8,493
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	(695)	472	(343)	713
Ending balance as of September 30,	11,673	9,206	11,673	9,206
Loans:
Individually evaluated for impairment					4,538	661
Collectively evaluated for impairment					3,142,983	2,905,128
Loans receivable, gross					3,150,298	2,909,439
Allowance for loan losses:
Individually evaluated for impairment					195	0
Collectively evaluated for impairment					11,478	12,016
Total Allowance for loan losses	12,368	8,734	12,016	8,493	11,673	12,016
Multi-family | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					2,777	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 June 30,	10,370	14,062	8,864	4,784
Charge-offs	(237)	(5,559)	(774)	(6,793)
Recoveries	62	248	173	351
Provision for loan losses	832	1,678	2,764	12,087
Ending balance as of September 30,	11,027	10,429	11,027	10,429
Loans:
Individually evaluated for impairment					30,275	17,621
Collectively evaluated for impairment					873,825	783,986
Loans receivable, gross					905,250	803,159
Allowance for loan losses:
Individually evaluated for impairment					3,119	1,990
Collectively evaluated for impairment					7,771	6,650
Total Allowance for loan losses	10,370	14,062	8,864	4,784	11,027	8,864
Commercial and industrial | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					1,150	1,552
Allowance for loan losses:
Loans acquired with credit deterioration					137	224
Commercial real estate - owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	1,582	3,651	1,348	4,336
Charge-offs	0	(35)	0	(378)
Recoveries	0	13	0	14
Provision for loan losses	305	(370)	539	(713)
Ending balance as of September 30,	1,887	3,259	1,887	3,259
Loans:
Individually evaluated for impairment					10,523	8,329
Collectively evaluated for impairment					368,030	286,951
Loans receivable, gross					391,471	308,241
Allowance for loan losses:
Individually evaluated for impairment					0	1
Collectively evaluated for impairment					1,857	1,347
Total Allowance for loan losses	1,582	3,651	1,348	4,336	1,887	1,348
Commercial real estate - owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					12,918	12,961
Allowance for loan losses:
Loans acquired with credit deterioration					30	0
Commercial real estate - non-owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	8,483	6,310	8,420	9,198
Charge-offs	(140)	(82)	(140)	(327)
Recoveries	0	0	8	0
Provision for loan losses	3	(109)	58	(2,752)
Ending balance as of September 30,	8,346	6,119	8,346	6,119
Loans:
Individually evaluated for impairment					10,659	4,831
Collectively evaluated for impairment					1,133,517	939,368
Loans receivable, gross					1,151,099	956,255
Allowance for loan losses:
Individually evaluated for impairment					27	148
Collectively evaluated for impairment					4,581	3,858
Total Allowance for loan losses	8,483	6,310	8,420	9,198	8,346	8,420
Commercial real estate - non-owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					6,923	12,056
Allowance for loan losses:
Loans acquired with credit deterioration					3,738	4,414
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	1,209	844	1,074	1,047
Charge-offs	0	0	0	(1,064)
Recoveries	8	8	465	195
Provision for loan losses	(168)	258	(490)	932
Ending balance as of September 30,	1,049	1,110	1,049	1,110
Loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					83,835	87,006
Loans receivable, gross					83,835	87,240
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					1,049	1,074
Total Allowance for loan losses	1,209	844	1,074	1,047	1,049	1,074
Construction | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					0	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 June 30,	3,535	3,455	3,298	2,698
Charge-offs	(43)	(256)	(456)	(282)
Recoveries	298	0	299	572
Provision for loan losses	(411)	(5)	238	206
Ending balance as of September 30,	3,379	3,194	3,379	3,194
Loans:
Individually evaluated for impairment					3,999	4,726
Collectively evaluated for impairment					215,187	258,446
Loans receivable, gross					227,122	271,613
Allowance for loan losses:
Individually evaluated for impairment					63	84
Collectively evaluated for impairment					2,515	2,141
Total Allowance for loan losses	3,535	3,455	3,298	2,698	3,379	3,298
Residential real estate | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					7,936	8,441
Allowance for loan losses:
Loans acquired with credit deterioration					801	1,073
Manufactured housing
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	440	316	494	262
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	(18)	70	(72)	124
Ending balance as of September 30,	422	386	422	386
Loans:
Individually evaluated for impairment					9,091	8,300
Collectively evaluated for impairment					92,186	101,838
Loans receivable, gross					104,404	113,490
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					95	98
Total Allowance for loan losses	440	316	494	262	422	494
Manufactured housing | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					3,127	3,352
Allowance for loan losses:
Loans acquired with credit deterioration					327	396
Other
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance as of June 30,	110	119	133	114
Charge-offs	(246)	0	(478)	(36)
Recoveries	10	6	10	91
Provision for loan losses	240	(5)	449	(49)
Ending balance as of September 30,	114	120	114	120
Loans:
Individually evaluated for impairment					42	140
Collectively evaluated for impairment					3,135	3,334
Loans receivable, gross					3,420	3,708
Allowance for loan losses:
Individually evaluated for impairment					0	50
Collectively evaluated for impairment					57	28
Total Allowance for loan losses	$ 110	$ 119	$ 133	$ 114	114	133
Other | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					243	234
Allowance for loan losses:
Loans acquired with credit deterioration					$ 57	$ 55