Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2018	$ 1,591,453	$ 13,717	$ 309,545	$ 1,323,870	$ (55,679)
Balance (in shares) at Dec. 31, 2018		65,834,395
Net income per consolidated statements of income	33,339			33,339
Other comprehensive income (loss), net of tax	14,764				14,764
Common stock dividends paid ($0.23 per share)	(15,033)			(15,033)
Shares withheld to pay taxes, long-term incentive plan	(1,604)	$ 25	(1,629)
Shares withheld to pay taxes, long-term incentive plan (in shares)		123,821
Repurchase and retirement of common stock	(36,893)	$ (243)	(36,650)
Repurchase and retirement of common stock (in shares)		(1,168,273)
Compensation expense, long-term incentive plan	1,002		1,002
Balance at Mar. 31, 2019	1,587,028	$ 13,499	272,268	1,342,176	(40,915)
Balance (in shares) at Mar. 31, 2019		64,789,943
Balance at Dec. 31, 2018	1,591,453	$ 13,717	309,545	1,323,870	(55,679)
Balance (in shares) at Dec. 31, 2018		65,834,395
Net income per consolidated statements of income	75,479
Other comprehensive income (loss), net of tax	30,863
Compensation expense, long-term incentive plan	2,281
Balance at Jun. 30, 2019	1,618,550	$ 13,418	260,619	1,369,329	(24,816)
Balance (in shares) at Jun. 30, 2019		64,398,846
Balance at Mar. 31, 2019	1,587,028	$ 13,499	272,268	1,342,176	(40,915)
Balance (in shares) at Mar. 31, 2019		64,789,943
Net income per consolidated statements of income	42,140			42,140
Other comprehensive income (loss), net of tax	16,099				16,099
Common stock dividends paid ($0.23 per share)	(14,987)			(14,987)
Shares withheld to pay taxes, long-term incentive plan	(1)	$ 2	(3)
Shares withheld to pay taxes, long-term incentive plan (in shares)		7,087
Repurchase and retirement of common stock	(13,008)	$ (83)	(12,925)
Repurchase and retirement of common stock (in shares)		(398,184)
Compensation expense, long-term incentive plan	1,279		1,279
Balance at Jun. 30, 2019	1,618,550	$ 13,418	260,619	1,369,329	(24,816)
Balance (in shares) at Jun. 30, 2019		64,398,846
Balance at Dec. 31, 2019	$ 1,660,702	$ 13,376	256,400	1,414,526	(23,600)
Balance (in shares) at Dec. 31, 2019	64,200,111	64,200,111
FASB ASU 2016-13 adoption adjustment	$ (19,949)			(19,949)
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	$ 13,376	256,400	1,414,526	(23,600)
Balance (in shares) at Dec. 31, 2019	64,200,111	64,200,111
Net income per consolidated statements of income	$ 54,368
Other comprehensive income (loss), net of tax	34,165
Compensation expense, long-term incentive plan	2,668
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	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	63,422,439