Loans and Leases Receivable and Allowance for Loan and Lease Losses - Schedule of Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 48,388	$ 38,288	$ 39,972	$ 38,015
Charge-offs	(2,200)	(527)	(4,794)	(2,377)
Recoveries	439	56	1,336	846
Provision for loan and lease losses	4,426	2,924	14,539	4,257
Ending balance	51,053	40,741	51,053	40,741
Loans:
Individually evaluated for impairment					$ 27,668	$ 39,118
Collectively evaluated for impairment					7,292,498	7,077,806
Loans and leases receivable, gross					7,338,555	7,138,498
Loans receivable, at amortized cost or lower of cost or market					7,338,555	7,138,498
Allowance for loan losses:
Individually evaluated for impairment					395	845
Collectively evaluated for impairment					48,034	36,249
Total Allowance for loan losses	51,053	38,288	51,053	40,741	51,053	39,972
Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					18,389	21,574
Loans and leases receivable, gross					18,389	21,574
Allowance for loan losses:
Loans acquired with credit deterioration					2,624	2,878
Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	9,926	12,069	11,462	12,168
Charge-offs	0	0	(541)	0
Recoveries	0	0	7	0
Provision for loan and lease losses	(2,428)	(240)	(3,430)	(339)
Ending balance	7,498	11,829	7,498	11,829
Loans:
Individually evaluated for impairment					0	1,155
Collectively evaluated for impairment					2,298,588	3,282,452
Loans and leases receivable, gross					2,300,244	3,285,297
Allowance for loan losses:
Individually evaluated for impairment					0	539
Collectively evaluated for impairment					7,498	10,923
Total Allowance for loan losses	9,926	12,069	11,462	11,829	7,498	11,462
Multi-family | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					1,656	1,690
Loans and leases receivable, gross					1,656	1,690
Allowance for loan losses:
Loans acquired with credit deterioration					0	0
Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	13,736	12,258	12,145	10,918
Charge-offs	(349)	(90)	(532)	(314)
Recoveries	369	30	826	205
Provision for loan and lease losses	2,119	516	3,436	1,905
Ending balance	15,875	12,714	15,875	12,714
Loans:
Individually evaluated for impairment					5,375	17,828
Collectively evaluated for impairment					1,882,385	1,355,436
Loans and leases receivable, gross					1,888,134	1,373,800
Allowance for loan losses:
Individually evaluated for impairment					167	261
Collectively evaluated for impairment					15,448	11,516
Total Allowance for loan losses	13,736	12,258	15,875	12,714	15,875	12,145
Commercial and industrial | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					374	536
Loans and leases receivable, gross					374	536
Allowance for loan losses:
Loans acquired with credit deterioration					260	368
Commercial real estate owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,360	2,988	3,320	3,232
Charge-offs	(45)	0	(119)	(501)
Recoveries	10	0	235	326
Provision for loan and lease losses	(435)	164	(546)	95
Ending balance	2,890	3,152	2,890	3,152
Loans:
Individually evaluated for impairment					2,084	1,069
Collectively evaluated for impairment					466,604	567,970
Loans and leases receivable, gross					475,465	577,477
Allowance for loan losses:
Individually evaluated for impairment					0	1
Collectively evaluated for impairment					2,882	3,319
Total Allowance for loan losses	3,360	2,988	2,890	3,152	2,890	3,320
Commercial real estate owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					6,777	8,438
Loans and leases receivable, gross					6,777	8,438
Allowance for loan losses:
Loans acquired with credit deterioration					8	0
Commercial real estate non-owner occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,159	6,698	6,093	7,437
Charge-offs	0	0	0	0
Recoveries	0	5	0	5
Provision for loan and lease losses	281	(254)	347	(993)
Ending balance	6,440	6,449	6,440	6,449
Loans:
Individually evaluated for impairment					83	129
Collectively evaluated for impairment					1,264,361	1,120,633
Loans and leases receivable, gross					1,268,557	1,125,106
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					4,555	4,161
Total Allowance for loan losses	6,159	6,698	6,440	6,449	6,440	6,093
Commercial real estate non-owner occupied | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					4,113	4,344
Loans and leases receivable, gross					4,113	4,344
Allowance for loan losses:
Loans acquired with credit deterioration					1,885	1,932
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	649	992	624	979
Charge-offs	0	0	0	0
Recoveries	8	11	128	231
Provision for loan and lease losses	1	59	(94)	(148)
Ending balance	658	1,062	658	1,062
Loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					61,200	56,491
Loans and leases receivable, gross					61,200	56,491
Allowance for loan losses:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					658	624
Total Allowance for loan losses	649	992	624	1,062	658	624
Construction | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					0	0
Loans and leases receivable, gross					0	0
Allowance for loan losses:
Loans acquired with credit deterioration					0	0
Residential real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,168	2,908	3,654	2,929
Charge-offs	0	0	(109)	(407)
Recoveries	5	6	20	69
Provision for loan and lease losses	(90)	987	518	1,310
Ending balance	4,083	3,901	4,083	3,901
Loans:
Individually evaluated for impairment					9,057	8,631
Collectively evaluated for impairment					616,054	553,593
Loans and leases receivable, gross					628,786	566,561
Allowance for loan losses:
Individually evaluated for impairment					40	41
Collectively evaluated for impairment					3,727	3,227
Total Allowance for loan losses	4,168	2,908	3,654	2,929	4,083	3,654
Residential real estate | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					3,675	4,337
Loans and leases receivable, gross					3,675	4,337
Allowance for loan losses:
Loans acquired with credit deterioration					316	386
Manufactured housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	123	149	145	180
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan and lease losses	904	(55)	882	(86)
Ending balance	1,027	94	1,027	94
Loans:
Individually evaluated for impairment					9,929	10,195
Collectively evaluated for impairment					61,096	67,528
Loans and leases receivable, gross					72,616	79,731
Allowance for loan losses:
Individually evaluated for impairment					123	3
Collectively evaluated for impairment					904	89
Total Allowance for loan losses	123	149	145	94	1,027	145
Manufactured housing | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					1,591	2,008
Loans and leases receivable, gross					1,591	2,008
Allowance for loan losses:
Loans acquired with credit deterioration					0	53
Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	10,267	226	2,529	172
Charge-offs	(1,806)	(437)	(3,493)	(1,155)
Recoveries	47	4	120	10
Provision for loan and lease losses	4,074	1,747	13,426	2,513
Ending balance	12,582	1,540	12,582	1,540
Loans:
Individually evaluated for impairment					1,140	111
Collectively evaluated for impairment					642,210	73,703
Loans and leases receivable, gross					643,553	74,035
Allowance for loan losses:
Individually evaluated for impairment					65	0
Collectively evaluated for impairment					12,362	2,390
Total Allowance for loan losses	$ 10,267	$ 226	$ 2,529	$ 172	12,582	2,529
Other consumer | Purchased Credit Impaired Loans
Loans:
Loans acquired with credit deterioration					203	221
Loans and leases receivable, gross					203	221
Allowance for loan losses:
Loans acquired with credit deterioration					$ 155	$ 139