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
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Allowance for loan losses:
Balance at beginning of period	$ 15,721	$ 15,183
Provision (benefit) charged to operations	1,371	700
Charge-offs	(533)	(205)
Recoveries	258	473
Balance at end of period	16,817	16,151
Ending allowance balance attributed to loans:
Individually evaluated for impairment	1,605		$ 0
Collectively evaluated for impairment	15,212		15,721
Total ending allowance balance	16,817		15,721
Loans:
Loans individually evaluated for impairment	44,060		46,988
Loans collectively evaluated for impairment	5,366,433		3,927,414
Total loans	5,410,493		3,974,402
Residential Real Estate
Allowance for loan losses:
Balance at beginning of period	1,804	2,245
Provision (benefit) charged to operations	493	(627)
Charge-offs	(244)	(49)
Recoveries	85	0
Balance at end of period	2,138	1,569
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	2,138		1,804
Total ending allowance balance	2,138		1,804
Loans:
Loans individually evaluated for impairment	11,406		10,605
Loans collectively evaluated for impairment	1,868,881		1,737,985
Total loans	1,880,287		1,748,590
Commercial Real Estate - Owner Occupied
Allowance for loan losses:
Balance at beginning of period	3,175	2,999
Provision (benefit) charged to operations	(307)	390
Charge-offs	0	(50)
Recoveries	3
Balance at end of period	2,871	3,449
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	2,871		3,175
Total ending allowance balance	2,871		3,175
Loans:
Loans individually evaluated for impairment	9,811		15,132
Loans collectively evaluated for impairment	752,830		554,365
Total loans	762,641		569,497
Commercial Real Estate - Investor
Allowance for loan losses:
Balance at beginning of period	7,952	6,361
Provision (benefit) charged to operations	879	993
Charge-offs	(123)	0
Recoveries	130	7
Balance at end of period	8,838	7,361
Ending allowance balance attributed to loans:
Individually evaluated for impairment	930		0
Collectively evaluated for impairment	7,908		7,952
Total ending allowance balance	8,838		7,952
Loans:
Loans individually evaluated for impairment	18,085		17,923
Loans collectively evaluated for impairment	2,007,466		1,168,379
Total loans	2,025,551		1,186,302
Consumer
Allowance for loan losses:
Balance at beginning of period	614	1,110
Provision (benefit) charged to operations	(1)	20
Charge-offs	(122)	(18)
Recoveries	16	24
Balance at end of period	507	1,136
Ending allowance balance attributed to loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	507		614
Total ending allowance balance	507		614
Loans:
Loans individually evaluated for impairment	2,489		2,464
Loans collectively evaluated for impairment	369,685		279,904
Total loans	372,174		282,368
Commercial and Industrial
Allowance for loan losses:
Balance at beginning of period	1,801	2,037
Provision (benefit) charged to operations	470	(201)
Charge-offs	(44)	(88)
Recoveries	24	332
Balance at end of period	2,251	2,080
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	1,576		1,801
Total ending allowance balance	2,251		1,801
Loans:
Loans individually evaluated for impairment	2,269		864
Loans collectively evaluated for impairment	367,571		186,781
Total loans	369,840		187,645
Unallocated
Allowance for loan losses:
Balance at beginning of period	375	431
Provision (benefit) charged to operations	(163)	125
Balance at end of period	212	$ 556
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	212		375
Total ending allowance balance	212		375
Loans:
Total loans	$ 0		$ 0