Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect Period Of Adoption Adjustment [Member]	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect Period Of Adoption Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2019	$ 1,660,702	$ (19,949)	$ 13,376	$ 256,400	$ 1,414,526	$ (19,949)	$ (23,600)
Balance (in shares) at Dec. 31, 2019			64,200,111
Accounting standards update [Extensible List]	ASU 2016-13 [Member]
Net income per consolidated statements of income	$ 22,218				22,218
Other comprehensive income (loss), net of tax	31,298						31,298
Common stock dividends paid ($0.23 per share)	(14,706)				(14,706)
Shares withheld to pay taxes, long-term incentive plan	(1,020)		$ 17	(1,037)
Shares withheld to pay taxes, long-term incentive plan (in shares)			83,759
Repurchase and retirement of common stock	(27,538)		$ (184)	(27,354)
Repurchase and retirement of common stock (in shares)			(886,958)
Compensation expense, long-term incentive plan	1,394			1,394
Balance at Mar. 31, 2020	1,652,399		$ 13,209	229,403	1,402,089		7,698
Balance (in shares) at Mar. 31, 2020			63,396,912
Balance at Dec. 31, 2020	$ 1,741,117		$ 13,215	233,120	1,495,833		(1,051)
Balance (in shares) at Dec. 31, 2020	63,424,526		63,424,526
Net income per consolidated statements of income	$ 51,962				51,962
Other comprehensive income (loss), net of tax	(15,455)						(15,455)
Common stock dividends paid ($0.23 per share)	(14,685)				(14,685)
Shares withheld to pay taxes, long-term incentive plan	(1,230)		$ 24	(1,254)
Shares withheld to pay taxes, long-term incentive plan (in shares)			114,977
Repurchase and retirement of common stock	(4,185)		$ (30)	(4,155)
Repurchase and retirement of common stock (in shares)			(144,981)
Compensation expense, long-term incentive plan	2,181			2,181
Balance at Mar. 31, 2021	$ 1,759,705		$ 13,209	$ 229,892	$ 1,533,110		$ (16,506)
Balance (in shares) at Mar. 31, 2021	63,394,522		63,394,522