Parent Company Only Financial Information - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dividends from:
Income tax benefit									$ (8,560)	$ (6,510)	$ (12,392)
Net Income	$ 10,484	$ 10,357	$ 9,767	$ 9,473	$ 8,945	$ 9,236	$ 8,441	$ 7,097	40,081	33,719	23,860
Parent Company
Dividends from:
Bank subsidiary									12,696	12,029	8,840
Non-bank subsidiaries									0	3,000	2,250
Other									232	212	220
Total income									12,928	15,241	11,310
Expenses									(5,518)	(5,184)	(4,957)
Income before income taxes and equity in undistributed net income of subsidiaries									7,410	10,057	6,353
Income tax benefit									1,177	1,116	1,614
Equity in undistributed net income of bank subsidiary									27,580	24,031	17,430
Equity in undistributed (distributions in excess) of net income of non-bank subsidiaries									3,914	(1,485)	(1,537)
Net Income									$ 40,081	$ 33,719	$ 23,860