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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Balance at beginning of period	$ 16,691	$ 16,557	$ 15,721	$ 15,183
Provision (benefit) charged to operations	907	1,165	2,984	3,030
Charge-offs	(891)	(1,357)	(2,708)	(2,861)
Recoveries	114	219	824	1,232
Balance at end of period	16,821	16,584	16,821	16,584
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		$ 0
Collectively evaluated for impairment	16,821		16,821		15,721
Total ending allowance balance	16,821		16,821		15,721
Loans:
Loans individually evaluated for impairment	33,088		33,088		46,988
Loans collectively evaluated for impairment	5,509,285		5,509,285		3,927,414
Total loans	5,542,373		5,542,373		3,974,402
Commercial and Industrial
Allowance for loan losses:
Balance at beginning of period	2,080	2,253	1,801	2,037
Provision (benefit) charged to operations	(520)	(180)	(238)	(221)
Charge-offs	(146)	(6)	(202)	(94)
Recoveries	28	50	81	395
Balance at end of period	1,442	2,117	1,442	2,117
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,442		1,442		1,801
Total ending allowance balance	1,442		1,442		1,801
Loans:
Loans individually evaluated for impairment	1,738		1,738		864
Loans collectively evaluated for impairment	340,817		340,817		186,781
Total loans	342,555		342,555		187,645
Commercial Real Estate - Owner Occupied
Allowance for loan losses:
Balance at beginning of period	2,340	3,097	3,175	2,999
Provision (benefit) charged to operations	187	119	(734)	167
Charge-offs	0	0	(91)	(73)
Recoveries	1	0	178	123
Balance at end of period	2,528	3,216	2,528	3,216
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	2,528		2,528		3,175
Total ending allowance balance	2,528		2,528		3,175
Loans:
Loans individually evaluated for impairment	5,446		5,446		15,132
Loans collectively evaluated for impairment	729,274		729,274		554,365
Total loans	734,720		734,720		569,497
Commercial Real Estate - Investor
Allowance for loan losses:
Balance at beginning of period	9,058	8,367	7,952	6,361
Provision (benefit) charged to operations	661	81	2,706	2,164
Charge-offs	(138)	0	(1,239)	(84)
Recoveries	9	24	171	31
Balance at end of period	9,590	8,472	9,590	8,472
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	9,590		9,590		7,952
Total ending allowance balance	9,590		9,590		7,952
Loans:
Loans individually evaluated for impairment	12,760		12,760		17,923
Loans collectively evaluated for impairment	1,999,137		1,999,137		1,168,379
Total loans	2,011,897		2,011,897		1,186,302
Residential Real Estate
Allowance for loan losses:
Balance at beginning of period	2,126	1,492	1,804	2,245
Provision (benefit) charged to operations	578	1,465	1,079	1,477
Charge-offs	(535)	(1,284)	(936)	(2,485)
Recoveries	57	128	279	564
Balance at end of period	2,226	1,801	2,226	1,801
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	2,226		2,226		1,804
Total ending allowance balance	2,226		2,226		1,804
Loans:
Loans individually evaluated for impairment	10,454		10,454		10,605
Loans collectively evaluated for impairment	2,009,464		2,009,464		1,737,985
Total loans	2,019,918		2,019,918		1,748,590
Consumer
Allowance for loan losses:
Balance at beginning of period	526	930	614	1,110
Provision (benefit) charged to operations	57	(122)	41	(346)
Charge-offs	(72)	(67)	(240)	(125)
Recoveries	19	17	115	119
Balance at end of period	530	758	530	758
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	530		530		614
Total ending allowance balance	530		530		614
Loans:
Loans individually evaluated for impairment	2,690		2,690		2,464
Loans collectively evaluated for impairment	430,593		430,593		279,904
Total loans	433,283		433,283		282,368
Unallocated
Allowance for loan losses:
Balance at beginning of period	561	418	375	431
Provision (benefit) charged to operations	(56)	(198)	130	(211)
Balance at end of period	505	$ 220	505	$ 220
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	505		505		375
Total ending allowance balance	505		505		375
Loans:
Total loans	$ 0		$ 0		$ 0