Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Base salaries, net of deferred loan origination costs	$ 17,211	$ 14,429	$ 33,968	$ 28,391
Incentive compensation	3,706	2,159	6,273	4,611
Benefits and other compensation costs	5,802	4,865	11,606	10,103
Total salaries and benefits expense	26,719	21,453	51,847	43,105
Occupancy	3,738	2,720	7,512	5,401
Data processing and software	3,354	2,679	6,703	5,193
Equipment	1,752	1,637	3,619	3,188
Intangible amortization	1,431	339	2,862	678
Advertising	1,533	1,035	2,864	1,873
ATM and POS network charges	1,270	1,437	2,593	2,663
Professional fees	1,057	774	1,896	1,546
Telecommunications	773	681	1,570	1,382
Regulatory assessments and insurance	490	417	1,001	847
Merger and acquisition expense		601		1,077
Postage	315	301	625	659
Operational losses	226	252	451	546
Courier service	412	224	682	491
Other miscellaneous expense	3,782	3,320	8,140	7,383
Total other noninterest expense	20,133	16,417	40,518	32,927
Total noninterest expense	$ 46,852	$ 37,870	$ 92,365	$ 76,032