Condensed Financial Information - Parent Company Only - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and due from banks	$ 208,599	$ 142,933	$ 175,801	$ 118,493
Equity securities	638,618	628,046
Investment securities, held to maturity	153,646	139,685
Other assets	42,308	35,576
TOTAL ASSETS	5,806,093	5,405,639
LIABILITIES AND STOCKHOLDERS’ EQUITY
Other liabilities	41,634	31,920
Subordinated debentures	105,027	104,902
Total stockholders’ equity	623,739	583,122	550,044	400,516
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	5,806,093	5,405,639
Parent Company
ASSETS
Cash and due from banks	23,285	17,695	$ 11,675	$ 15,921
Equity securities	2,743	5,158
Investment securities, held to maturity	1,000	1,000
Investment in subsidiaries	695,571	659,180
Other assets	7,182	6,013
TOTAL ASSETS	729,781	689,046
LIABILITIES AND STOCKHOLDERS’ EQUITY
Other liabilities	1,015	1,022
Subordinated debentures	105,027	104,902
Total stockholders’ equity	623,739	583,122
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 729,781	$ 689,046