Condensed Financial Information - Parent Company Only - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities
Net Income	$ 57,518	$ 70,672	$ 63,401
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Gain on sale of equity securities	(1,213)	0	0
Provision for credit losses	27,222	2,130	4,413
Change in market value of equity securities	552	(496)	583
Excess tax (deficiencies) benefits	(132)	189	318
Increase in other assets	(56,639)	(15,986)	2,679
Increase (decrease) in other liabilities	50,434	15,092	9,743
Net Cash Provided by Operating Activities	84,991	87,131	79,438
Cash Flows from Investing Activities
Purchase of equity securities	(2,772)	(1,343)	(570)
Proceeds from repayments and maturities of held to maturity securities	38,941	31,457	26,083
Proceeds from sales of equity securities	4,148	1,287	2,155
Net cash received from business acquisition	0	13,454	0
Net Cash Used in Investing Activities:	(928,022)	(303,977)	(342,558)
Cash Flows from Financing Activities
Cash dividends paid on common stock	(25,457)	(24,919)	(21,307)
Purchase of treasury stock	(1,452)	0	0
Retirement of restricted stock	(501)	(715)	(763)
Exercise of stock options	0	313	307
Net Cash Provided by Financing Activities:	830,750	290,618	328,786
Net (decrease) increase in cash and cash equivalents	(12,281)	73,772	65,666
Cash and cash equivalents, beginning of year	282,371	208,599	142,933
Cash and Cash Equivalents, End of Year	270,090	282,371	208,599
Parent Company
Cash Flows from Operating Activities
Net Income	57,518	70,672	63,401
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Gain on sale of equity securities	(149)	0	0
Amortization of subordinated debt costs	37	36	125
Provision for credit losses	(12)	0	0
Change in market value of equity securities	786	(197)	338
Excess tax (deficiencies) benefits	(132)	189	318
Increase in other assets	(1,462)	(1,873)	(1,446)
Increase (decrease) in other liabilities	25	121	(6)
Equity in undistributed income of subsidiaries	(32,915)	(38,160)	(37,454)
Net Cash Provided by Operating Activities	23,696	30,788	25,276
Cash Flows from Investing Activities
Purchase of equity securities	(49)	(82)	(78)
Proceeds from repayments and maturities of held to maturity securities	1,000	0	0
Proceeds from sales of equity securities	1,148	1,287	2,155
Net cash received from business acquisition	0	24	0
Net Cash Used in Investing Activities:	2,099	1,229	2,077
Cash Flows from Financing Activities
Cash dividends paid on common stock	(25,457)	(24,919)	(21,307)
Retirement of restricted stock	(501)	(715)	(763)
Exercise of stock options	0	313	307
Net Cash Provided by Financing Activities:	(27,410)	(25,321)	(21,763)
Net (decrease) increase in cash and cash equivalents	(1,615)	6,696	5,590
Cash and cash equivalents, beginning of year	29,981	23,285	17,695
Cash and Cash Equivalents, End of Year	$ 28,366	$ 29,981	$ 23,285