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)								39,665
Dividend Reinvestment Plan								$ 1	845	0	0	0	846
Restricted stock units vested (in shares)								51,183
Restricted stock units vested								$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs								0	(523)	0	0	0	(523)
Stock -based compensation								0	1,543	0	0	0	1,543
Cash dividends								0	0	0	(24,660)	0	(24,660)
Other comprehensive income (loss)								0	0	7,575	0	0	7,575
Net income								$ 0	0	0	46,852	0	46,852
Purchases of treasury stock (in shares)								(400,000)
Purchases of treasury stock								$ 0	0	0	0	(12,880)	(12,880)
Balance (in shares) at Mar. 31, 2020								79,420,267
Ending balance, loss, net of tax at Mar. 31, 2020								$ 902	952,331	9,877	1,681,345	(331,418)	2,313,037
Balance (in shares) (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2020	[1]	0
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	$ (798)	$ 0	$ (798)
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)								20,036
Dividend Reinvestment Plan								$ 0	868	0	0	0	868
Restricted stock units vested (in shares)								66,724
Restricted stock units vested								$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs								0	(1,279)	0	0	0	(1,279)
Stock -based compensation								0	1,243	0	0	0	1,243
Cash dividends								0	0	0	(24,650)	0	(24,650)
Other comprehensive income (loss)								0	0	(3,624)	0	0	(3,624)
Net income								$ 0	0	0	73,384	0	73,384
Balance (in shares) at Mar. 31, 2021								79,595,025
Ending balance, loss, net of tax at Mar. 31, 2021								$ 907	$ 965,566	$ 1,686	$ 1,837,261	$ (342,131)	$ 2,463,289

[1] See "Accounting Standards Adopted in 2021" in Note 3 Recent Accounting Pronouncements, ASU 2016-13, Financial Instruments - Credit Losses (Topic 326).