Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($)		Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock Outstanding [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Treasury Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock Outstanding [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2019								79,729,419
Beginning balance, loss, net of tax at Dec. 31, 2019								$ 900,000	$ 950,466,000	$ 2,302,000	$ 1,659,153,000	$ (318,538,000)	$ 2,294,283,000
Dividend Reinvestment Plan (in shares)								72,568
Dividend Reinvestment Plan								$ 1,000	1,705,000	0	0	0	1,706,000
Restricted stock units vested (in shares)								186,887
Restricted stock units vested								$ 2,000	0	0	0	0	2,000
Shares withheld related to net share settlement of RSUs								0	(1,899,000)	0	0	0	(1,899,000)
Stock issued to directors								$ 0	800,000	0	0	0	800,000
Purchases of treasury stock (in shares)								(400,000)
Purchases of treasury stock								$ 0	0	0	0	(12,880,000)	(12,880,000)
Stock-based compensation								0	2,544,000	0	0	0	2,544,000
Cash dividends								0	0	0	(49,332,000)	0	(49,332,000)
Other comprehensive income (loss)								0	0	6,051,000	0	0	6,051,000
Net income								$ 0	0	0	101,173,000	0	101,173,000
Balance (in shares) at Jun. 30, 2020								79,619,984
Ending balance, loss, net of tax at Jun. 30, 2020								$ 903,000	953,616,000	8,353,000	1,710,994,000	(331,418,000)	2,342,448,000
Balance (in shares) at Mar. 31, 2020								79,420,267
Beginning balance, loss, net of tax at Mar. 31, 2020								$ 902,000	952,331,000	9,877,000	1,681,345,000	(331,418,000)	2,313,037,000
Dividend Reinvestment Plan (in shares)								32,903
Dividend Reinvestment Plan								$ 0	860,000	0	0	0	860,000
Restricted stock units vested (in shares)								135,704
Restricted stock units vested								$ 1,000	0	0	0	0	1,000
Shares withheld related to net share settlement of RSUs								$ 0	(1,376,000)	0	0	0	(1,376,000)
Stock issued to directors (in shares)								31,110
Stock issued to directors								$ 0	800,000	0	0	0	800,000
Stock-based compensation								0	1,001,000	0	0	0	1,001,000
Cash dividends								0	0	0	(24,672,000)	0	(24,672,000)
Other comprehensive income (loss)								0	0	(1,524,000)	0	0	(1,524,000)
Net income								$ 0	0	0	54,321,000	0	54,321,000
Balance (in shares) at Jun. 30, 2020								79,619,984
Ending balance, loss, net of tax at Jun. 30, 2020								$ 903,000	953,616,000	8,353,000	1,710,994,000	(331,418,000)	2,342,448,000
Balance (in shares) at Dec. 31, 2020								79,508,265
Beginning balance, loss, net of tax (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2020	[1]	$ 0	$ 0	$ 0	$ (3,139)	$ 0	$ (3,139)
Beginning balance, loss, net of tax at Dec. 31, 2020								$ 906,000	964,734,000	5,310,000	1,789,325,000	(342,131,000)	2,418,144,000
Dividend Reinvestment Plan (in shares)								40,059
Dividend Reinvestment Plan								$ 1,000	1,724,000	0	0	0	1,725,000
Restricted stock units vested (in shares)								121,922
Restricted stock units vested								$ 1,000	0	0	0	0	1,000
Shares withheld related to net share settlement of RSUs								$ 0	(2,594,000)	0	0	0	(2,594,000)
Stock issued to directors (in shares)								20,750
Stock issued to directors								$ 0	850,000	0	0	0	$ 850,000
Purchases of treasury stock (in shares)								(1,532,406)					(1,532,406)
Purchases of treasury stock								$ 0	0	0	0	(63,529,000)	$ (63,529,000)
Stock-based compensation								0	2,452,000	0	0	0	2,452,000
Cash dividends								0	0	0	(49,198,000)	0	(49,198,000)
Other comprehensive income (loss)								0	0	(2,938,000)	0	0	(2,938,000)
Net income								$ 0	0	0	150,583,000	0	150,583,000
Balance (in shares) at Jun. 30, 2021								78,158,590
Ending balance, loss, net of tax at Jun. 30, 2021								$ 908,000	967,166,000	2,372,000	1,887,571,000	(405,660,000)	2,452,357,000
Balance (in shares) at Mar. 31, 2021								79,595,025
Beginning balance, loss, net of tax at Mar. 31, 2021	[2]							$ 907,000	965,566,000	1,686,000	1,834,920,000	(342,131,000)	2,460,948,000
Dividend Reinvestment Plan (in shares)								20,023
Dividend Reinvestment Plan								$ 1,000	856,000	0	0	0	857,000
Restricted stock units vested (in shares)								55,198
Restricted stock units vested								$ 0	0	0	0	0	0
Shares withheld related to net share settlement of RSUs								$ 0	(1,315,000)	0	0	0	(1,315,000)
Stock issued to directors (in shares)								20,750
Stock issued to directors								$ 0	850,000	0	0	0	850,000
Purchases of treasury stock (in shares)								(1,532,406)
Purchases of treasury stock								$ 0	0	0	0	(63,529,000)	(63,529,000)
Stock-based compensation								0	1,209,000	0	0	0	1,209,000
Cash dividends								0	0	0	(24,548,000)	0	(24,548,000)
Other comprehensive income (loss)								0	0	686,000	0	0	686,000
Net income								$ 0	0	0	77,199,000	0	77,199,000
Balance (in shares) at Jun. 30, 2021								78,158,590
Ending balance, loss, net of tax at Jun. 30, 2021								$ 908,000	$ 967,166,000	$ 2,372,000	$ 1,887,571,000	$ (405,660,000)	$ 2,452,357,000

[1] Balance sheet amounts previously reported for the impact of the initial adoption of CECL on January 1, 2021 have been corrected. The correction had an after-tax decrease to the cumulative effect of the change in accounting principle related to ASC 326 of $2.3 million.

[2] Balance sheet amounts previously reported for the impact of the initial adoption of CECL on January 1, 2021 have been corrected. The correction had an after-tax decrease to the cumulative effect of the change in accounting principle related to ASC326 of $2.3 million.