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, 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
Net income per consolidated statements of income	54,368
Other comprehensive income (loss), net of tax	34,165
Balance at Jun. 30, 2020	1,673,944		$ 13,214	230,613	1,419,552		10,565
Balance (in shares) at Jun. 30, 2020			63,422,439
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
Net income per consolidated statements of income	32,150				32,150
Other comprehensive income (loss), net of tax	2,867						2,867
Common stock dividends paid ($0.23 per share)	(14,687)				(14,687)
Shares withheld to pay taxes, long-term incentive plan	(59)		$ 5	(64)
Shares withheld to pay taxes, long-term incentive plan (in shares)			25,527
Compensation expense, long-term incentive plan	1,274			1,274
Balance at Jun. 30, 2020	1,673,944		$ 13,214	230,613	1,419,552		10,565
Balance (in shares) at Jun. 30, 2020			63,422,439
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
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	$ 99,943
Other comprehensive income (loss), net of tax	(9,590)
Balance at Jun. 30, 2021	$ 1,779,309		$ 13,079	210,420	1,566,451		(10,641)
Balance (in shares) at Jun. 30, 2021	62,773,226		62,773,226
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
Net income per consolidated statements of income	47,981				47,981
Other comprehensive income (loss), net of tax	5,865						5,865
Common stock dividends paid ($0.23 per share)	(14,640)				(14,640)
Shares withheld to pay taxes, long-term incentive plan	(11)		$ 2	(13)
Shares withheld to pay taxes, long-term incentive plan (in shares)			8,524
Repurchase and retirement of common stock	(20,805)		$ (132)	(20,673)
Repurchase and retirement of common stock (in shares)			(629,820)
Compensation expense, long-term incentive plan	1,214			1,214
Balance at Jun. 30, 2021	$ 1,779,309		$ 13,079	$ 210,420	$ 1,566,451		$ (10,641)
Balance (in shares) at Jun. 30, 2021	62,773,226		62,773,226