Condensed Financial Information - Parent Company Only - Schedule of Condensed Balance Sheet (Detail) - USD ($) $ in Thousands		12 Months Ended
	Dec. 06, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Cash and due from banks		$ 46,721	$ 48,757	$ 32,356	$ 31,995
Investments in subsidiaries, at equity in net assets:
Other assets		154	20
Total assets		4,554,862	4,230,528
Liabilities:
Subordinated notes		94,331	94,087
Other liabilities		40,979	49,972
Total liabilities		3,951,488	3,725,319
Shareholders' equity:		603,374	505,209	361,574	284,554
Total liabilities and shareholders’ equity		4,554,862	4,230,528
Proceeds from public offering of common stock	$ 70,500	70,501	0	0
Parent Company [Member]
Assets:
Cash and due from banks		73,756	1,980	17,096	$ 3,120
Investments in securities		1,077	914
Investments in subsidiaries, at equity in net assets:
Bank		612,045	587,532
Non-banks		0	0
Other assets		32,399	32,124
Total assets		719,277	622,550
Liabilities:
Dividends payable		5,866	5,316
Subordinated notes		94,331	94,087
Other liabilities		15,706	17,938
Total liabilities		115,903	117,341
Shareholders' equity:		603,374	505,209
Total liabilities and shareholders’ equity		719,277	622,550
Proceeds from public offering of common stock		$ 70,501	$ 0	$ 0