Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands		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	$ 950,466	$ 2,302	$ 1,659,153	$ (318,538)	$ 2,294,283
Dividend Reinvestment Plan (in shares)								109,988
Dividend Reinvestment Plan								$ 2	2,571	0	0	0	2,573
Restricted stock units vested (in shares)								188,879
Restricted stock units vested								$ 2	0	0	0	0	2
Shares withheld related to net share settlement of RSUs								$ 0	(1,903)	0	0	0	(1,903)
Stock issued to directors (in shares)								31,110
Stock issued to directors								$ 0	800	0	0	0	800
Purchases of treasury stock (in shares)								(400,000)
Purchases of treasury stock								$ 0	0	0	0	(12,880)	(12,880)
Stock-based compensation								0	3,808	0	0	0	3,808
Cash dividends								0	0	0	(74,014)	0	(74,014)
Other comprehensive income (loss)								0	0	4,087	0	0	4,087
Net income								$ 0	0	0	157,967	0	157,967
Balance (in shares) at Sep. 30, 2020								79,659,396
Ending balance, loss, net of tax at Sep. 30, 2020								$ 904	955,742	6,389	1,743,106	(331,418)	2,374,723
Balance (in shares) at Jun. 30, 2020								79,619,984
Beginning balance, loss, net of tax at Jun. 30, 2020								$ 903	953,616	8,353	1,710,994	(331,418)	2,342,448
Dividend Reinvestment Plan (in shares)								37,420
Dividend Reinvestment Plan								$ 1	866	0	0	0	867
Restricted stock units vested (in shares)								1,992
Restricted stock units vested								$ 0	0	0	0	0	0
Shares withheld related to net share settlement of RSUs								$ 0	(4)	0	0	0	(4)
Stock issued to directors (in shares)								0
Stock issued to directors								$ 0	0	0	0	0	0
Stock-based compensation								0	1,264	0	0	0	1,264
Cash dividends								0	0	0	(24,682)	0	(24,682)
Other comprehensive income (loss)								0	0	(1,964)	0	0	(1,964)
Net income								$ 0	0	0	56,794	0	56,794
Balance (in shares) at Sep. 30, 2020								79,659,396
Ending balance, loss, net of tax at Sep. 30, 2020								$ 904	955,742	6,389	1,743,106	(331,418)	2,374,723
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		$ 0	$ 0	$ 0	$ (3,139)	$ 0	$ (3,139)
Beginning balance, loss, net of tax at Dec. 31, 2020								$ 906	964,734	5,310	1,789,325	(342,131)	2,418,144
Dividend Reinvestment Plan (in shares)								62,326
Dividend Reinvestment Plan								$ 1	2,618	0	0	0	2,619
Restricted stock units vested (in shares)								123,893
Restricted stock units vested								$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs								$ 0	(2,632)	0	0	0	(2,632)
Stock issued to directors (in shares)								20,750
Stock issued to directors								$ 0	850	0	0	0	850
Purchases of treasury stock (in shares)								(2,475,019)
Purchases of treasury stock								$ 0	0	0	0	(100,668)	(100,668)
Stock-based compensation								0	4,149	0	0	0	4,149
Cash dividends								0	0	0	(73,335)	0	(73,335)
Other comprehensive income (loss)								0	0	(5,678)	0	0	(5,678)
Net income								$ 0	0	0	222,980	0	222,980
Balance (in shares) at Sep. 30, 2021								77,240,215
Ending balance, loss, net of tax at Sep. 30, 2021								$ 908	969,719	(368)	1,935,831	(442,799)	2,463,291
Balance (in shares) at Jun. 30, 2021								78,158,590
Beginning balance, loss, net of tax at Jun. 30, 2021	[1]							$ 908	967,166	2,372	1,887,571	(405,660)	2,452,357
Dividend Reinvestment Plan (in shares)								22,267
Dividend Reinvestment Plan								$ 0	894	0	0	0	894
Restricted stock units vested (in shares)								1,971
Restricted stock units vested								$ 0	0	0	0	0	0
Shares withheld related to net share settlement of RSUs								$ 0	(38)	0	0	0	(38)
Stock issued to directors (in shares)								0
Stock issued to directors								$ 0	0	0	0	0	$ 0
Purchases of treasury stock (in shares)								(942,613)					(942,613)
Purchases of treasury stock								$ 0	0	0	0	(37,139)	$ (37,139)
Stock-based compensation								0	1,697	0	0	0	1,697
Cash dividends								0	0	0	(24,137)	0	(24,137)
Other comprehensive income (loss)								0	0	(2,740)	0	0	(2,740)
Net income								$ 0	0	0	72,397	0	72,397
Balance (in shares) at Sep. 30, 2021								77,240,215
Ending balance, loss, net of tax at Sep. 30, 2021								$ 908	$ 969,719	$ (368)	$ 1,935,831	$ (442,799)	$ 2,463,291

[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 ASC326 of $2.3 million.