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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 37,491	$ 28,186	$ 30,932	$ 23,998
Charge-offs	(5,932)	(792)	(8,880)	(2,733)
Recoveries	275	467	1,223	965
Provision for loan losses	1,989	3,222	10,548	8,853
Ending balance	33,823	31,083	33,823	31,083
Loans:
Individually evaluated for impairment					$ 37,440	$ 40,325
Collectively evaluated for impairment					4,686,413	4,214,719
Loans acquired with credit deterioration					44,726	56,617
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					4,768,579	4,311,661
Allowance for loan losses:
Individually evaluated for impairment					4,842	1,342
Collectively evaluated for impairment					22,939	22,575
Loans acquired with credit deterioration					6,042	7,015
Total Allowance for loan losses	37,491	28,186	30,932	23,998	33,823	30,932
Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	8,734	7,205	8,493	4,227
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	472	767	713	3,745
Ending balance	9,206	7,972	9,206	7,972
Loans:
Individually evaluated for impairment					405	0
Collectively evaluated for impairment					2,401,322	2,204,059
Loans acquired with credit deterioration					3,673	4,346
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					2,405,400	2,208,405
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					9,206	8,493
Loans acquired with credit deterioration					0	0
Total Allowance for loan losses	8,734	7,205	8,493	4,227	9,206	8,493
Commercial and industrial (including owner occupied commercial real estate)
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	14,062	3,341	4,784	2,674
Charge-offs	(5,559)	(91)	(6,793)	(536)
Recoveries	248	67	351	292
Provision for loan losses	1,678	1,187	12,087	2,074
Ending balance	10,429	4,504	10,429	4,504
Loans:
Individually evaluated for impairment					18,257	16,523
Collectively evaluated for impairment					664,063	530,119
Loans acquired with credit deterioration					1,620	3,293
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					683,940	549,935
Allowance for loan losses:
Individually evaluated for impairment					4,581	856
Collectively evaluated for impairment					5,625	3,766
Loans acquired with credit deterioration					223	162
Total Allowance for loan losses	14,062	3,341	4,784	2,674	10,429	4,784
Commercial real estate owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,651	2,826	4,336	2,517
Charge-offs	(35)	(64)	(378)	(318)
Recoveries	13	85	14	91
Provision for loan losses	(370)	301	(713)	858
Ending balance	3,259	3,148	3,259	3,148
Loans:
Individually evaluated for impairment					7,486	13,349
Collectively evaluated for impairment					262,762	206,352
Loans acquired with credit deterioration					13,770	16,033
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					284,018	235,734
Allowance for loan losses:
Individually evaluated for impairment					2	96
Collectively evaluated for impairment					1,167	1,756
Loans acquired with credit deterioration					2,090	2,484
Total Allowance for loan losses	3,651	2,826	4,336	2,517	3,259	4,336
Commercial real estate non-owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	6,310	10,060	9,198	8,961
Charge-offs	(82)	(214)	(327)	(1,120)
Recoveries	0	284	0	304
Provision for loan losses	(109)	1,069	(2,752)	3,054
Ending balance	6,119	11,199	6,119	11,199
Loans:
Individually evaluated for impairment					9,104	6,173
Collectively evaluated for impairment					890,870	817,333
Loans acquired with credit deterioration					12,997	15,804
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					912,971	839,310
Allowance for loan losses:
Individually evaluated for impairment					129	170
Collectively evaluated for impairment					3,700	6,580
Loans acquired with credit deterioration					2,290	2,448
Total Allowance for loan losses	6,310	10,060	9,198	8,961	6,119	9,198
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	844	2,187	1,047	2,385
Charge-offs	0	(284)	(1,064)	(284)
Recoveries	8	4	195	7
Provision for loan losses	258	(208)	932	(409)
Ending balance	1,110	1,699	1,110	1,699
Loans:
Individually evaluated for impairment					0	2,325
Collectively evaluated for impairment					89,382	44,483
Loans acquired with credit deterioration					234	2,910
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					89,616	49,718
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					1,106	424
Loans acquired with credit deterioration					4	623
Total Allowance for loan losses	844	2,187	1,047	2,385	1,110	1,047
Residential real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,455	2,028	2,698	2,490
Charge-offs	(256)	(139)	(282)	(442)
Recoveries	0	23	572	265
Provision for loan losses	(5)	217	206	(184)
Ending balance	3,194	2,129	3,194	2,129
Loans:
Individually evaluated for impairment					2,047	1,820
Collectively evaluated for impairment					261,366	285,608
Loans acquired with credit deterioration					8,735	9,967
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					272,148	297,395
Allowance for loan losses:
Individually evaluated for impairment					92	188
Collectively evaluated for impairment					2,010	1,436
Loans acquired with credit deterioration					1,092	1,074
Total Allowance for loan losses	3,455	2,028	2,698	2,490	3,194	2,698
Manufactured housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	316	401	262	614
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	70	(80)	124	(293)
Ending balance	386	321	386	321
Loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					113,284	122,715
Loans acquired with credit deterioration					3,458	4,016
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					116,742	126,731
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					97	92
Loans acquired with credit deterioration					289	170
Total Allowance for loan losses	316	401	262	614	386	262
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	119	$ 138	114	130
Charge-offs	0		(36)	(33)
Recoveries	6	$ 4	91	6
Provision for loan losses	(5)	(31)	(49)	8
Ending balance	120	111	120	111
Loans:
Individually evaluated for impairment					141	135
Collectively evaluated for impairment					3,364	4,050
Loans acquired with credit deterioration					239	248
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered					3,744	4,433
Allowance for loan losses:
Individually evaluated for impairment					38	32
Collectively evaluated for impairment					28	28
Loans acquired with credit deterioration					54	54
Total Allowance for loan losses	$ 119	$ 138	$ 114	$ 130	$ 120	$ 114