Loans Receivable, Net - Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment and Based on Impairment Method Excluding PCI Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Allowance for loan losses:
Balance at beginning of period	$ 16,135	$ 16,691	$ 16,577	$ 15,721
Provision (benefit) charged to operations	305	907	1,281	2,984
Charge-offs	(353)	(891)	(2,359)	(2,708)
Recoveries	549	114	1,137	824
Balance at end of period	16,636	16,821	16,636	16,821
Ending allowance balance attributed to loans:
Individually evaluated for impairment	547		547		$ 0
Collectively evaluated for impairment	16,089		16,089		16,577
Total ending allowance balance	16,636		16,636		16,577
Loans:
Loans individually evaluated for impairment	27,817		27,817		29,797
Loans collectively evaluated for impairment	6,049,035		6,049,035		5,550,015
Total loans	6,076,852		6,076,852		5,579,812
Commercial and Industrial
Allowance for loan losses:
Balance at beginning of period	1,639	2,080	1,609	1,801
Provision (benefit) charged to operations	(352)	(520)	(406)	(238)
Charge-offs	0	(146)	0	(202)
Recoveries	49	28	133	81
Balance at end of period	1,336	1,442	1,336	1,442
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	1,336		1,336		1,609
Total ending allowance balance	1,336		1,336		1,609
Loans:
Loans individually evaluated for impairment	246		246		1,626
Loans collectively evaluated for impairment	405,724		405,724		303,368
Total loans	405,970		405,970		304,994
Commercial real estate – owner occupied
Allowance for loan losses:
Balance at beginning of period	2,868	2,340	2,277	3,175
Provision (benefit) charged to operations	80	187	1,192	(734)
Charge-offs	(142)	0	(663)	(91)
Recoveries	114	1	114	178
Balance at end of period	2,920	2,528	2,920	2,528
Ending allowance balance attributed to loans:
Individually evaluated for impairment	547		547		0
Collectively evaluated for impairment	2,373		2,373		2,277
Total ending allowance balance	2,920		2,920		2,277
Loans:
Loans individually evaluated for impairment	6,152		6,152		5,395
Loans collectively evaluated for impairment	780,700		780,700		734,980
Total loans	786,852		786,852		740,375
Commercial Real Estate – Investor
Allowance for loan losses:
Balance at beginning of period	8,406	9,058	8,770	7,952
Provision (benefit) charged to operations	711	661	26	2,706
Charge-offs	(57)	(138)	(143)	(1,239)
Recoveries	292	9	699	171
Balance at end of period	9,352	9,590	9,352	9,590
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	9,352		9,352		8,770
Total ending allowance balance	9,352		9,352		8,770
Loans:
Loans individually evaluated for impairment	7,975		7,975		9,738
Loans collectively evaluated for impairment	2,212,824		2,212,824		2,005,472
Total loans	2,220,799		2,220,799		2,015,210
Residential Real Estate
Allowance for loan losses:
Balance at beginning of period	1,966	2,126	2,413	1,804
Provision (benefit) charged to operations	193	578	899	1,079
Charge-offs	(27)	(535)	(1,221)	(936)
Recoveries	39	57	80	279
Balance at end of period	2,171	2,226	2,171	2,226
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	2,171		2,171		2,413
Total ending allowance balance	2,171		2,171		2,413
Loans:
Loans individually evaluated for impairment	10,093		10,093		10,064
Loans collectively evaluated for impairment	2,223,933		2,223,933		2,034,222
Total loans	2,234,026		2,234,026		2,044,286
Consumer
Allowance for loan losses:
Balance at beginning of period	512	526	486	614
Provision (benefit) charged to operations	10	57	185	41
Charge-offs	(127)	(72)	(332)	(240)
Recoveries	55	19	111	115
Balance at end of period	450	530	450	530
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	450		450		486
Total ending allowance balance	450		450		486
Loans:
Loans individually evaluated for impairment	3,351		3,351		2,974
Loans collectively evaluated for impairment	425,854		425,854		471,973
Total loans	429,205		429,205		474,947
Unallocated
Allowance for loan losses:
Balance at beginning of period	744	561	1,022	375
Provision (benefit) charged to operations	(337)	(56)	(615)	130
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Balance at end of period	407	$ 505	407	$ 505
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	407		407		1,022
Total ending allowance balance	407		407		1,022
Loans:
Loans individually evaluated for impairment	0		0		0
Loans collectively evaluated for impairment	0		0		0
Total loans	$ 0		$ 0		$ 0