Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Income and Expenses [Abstract]
Base salaries, net of deferred loan origination costs	$ 17,656	$ 15,685	$ 51,624	$ 44,076
Incentive compensation	3,791	4,515	10,064	9,126
Benefits and other compensation costs	5,452	5,623	17,058	15,726
Total salaries and benefits expense	26,899	25,823	78,746	68,928
Occupancy	3,711	3,173	11,223	8,574
Data processing and software	3,411	2,786	10,114	7,979
Equipment	1,679	1,750	5,298	4,938
Intangible amortization	1,431	1,390	4,293	2,068
Advertising	1,358	1,341	4,222	3,214
ATM and POS network charges	1,343	1,197	3,936	3,860
Professional fees	999	1,352	2,895	2,898
Telecommunications	867	819	2,437	2,201
Regulatory assessments and insurance	94	537	1,095	1,384
Merger and acquisition expense	0	4,150	0	5,227
Postage	438	275	1,063	934
Operational losses	228	217	679	763
Courier service	357	278	1,039	769
Gain on sale of foreclosed assets	(50)	(2)	(246)	(390)
Gain (Loss) on Disposition of Assets	2	152	82	206
Other miscellaneous expense	3,577	2,290	11,617	9,673
Total other non-interest expense	19,445	21,705	59,747	54,298
Total non-interest expense	$ 46,344	$ 47,528	$ 138,493	$ 123,226