Condensed Parent Company Financial Statements - Summary of Balance Sheet of Parent Company (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Cash	$ 280,518	$ 222,043
Goodwill	149,922	148,604	$ 79,749
Total assets	9,212,357	8,565,758	7,574,258
LIABILITIES AND STOCKHOLDERS' EQUITY
Other liabilities	51,864	49,230
Junior subordinated debentures	26,804	26,804
Stockholders’ equity	1,067,885	1,004,989	$ 902,789
Total liabilities and stockholders' equity	9,212,357	8,565,758
Parent Company [Member]
ASSETS
Cash	9,081	5,761
Investments in subsidiaries	1,003,017	946,311
Goodwill	69,478	69,478
Core deposit premium	8,622	9,617
Dividends receivable	12,750	11,622
Other assets	5,331	2,313
Total assets	1,108,279	1,045,102
LIABILITIES AND STOCKHOLDERS' EQUITY
Other liabilities	13,590	13,309
Junior subordinated debentures	26,804	26,804
Stockholders’ equity	1,067,885	1,004,989
Total liabilities and stockholders' equity	$ 1,108,279	$ 1,045,102