Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	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, 2018	80,501,948
Beginning balance, loss, net of tax at Dec. 31, 2018	$ 898	$ 942,062	$ (18,006)	$ 1,479,149	$ (282,237)	$ 2,121,866
Dividend Reinvestment Plan (in shares)	47,290
Dividend Reinvestment Plan	$ 1	1,680	0	0	0	1,681
Restricted stock units vested (in shares)	123,199
Restricted stock units vested	$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs	$ 0	(2,300)	0	0	0	(2,300)
Stock issued to directors (in shares)	21,160
Stock issued to directors	$ 0	749	0	0	0	749
Stock -based compensation	0	3,059	0	0	0	3,059
Cash dividends	0	0	0	(49,721)	0	(49,721)
Total other comprehensive (loss)/income, net of tax	0	0	16,648	0	0	16,648
Net income	$ 0	0	0	138,923	0	138,923
Purchases of treasury stock (in shares)	(875,594)
Purchases of treasury stock	$ 0	0	0	0	(31,609)	(31,609)
Balance (in shares) at Jun. 30, 2019	79,818,003
Ending balance, loss, net of tax at Jun. 30, 2019	$ 900	945,250	(1,358)	1,568,351	(313,846)	2,199,297
Balance (in shares) at Mar. 31, 2019	80,362,840
Beginning balance, loss, net of tax at Mar. 31, 2019	$ 899	942,838	(10,431)	1,520,861	(290,838)	2,163,329
Dividend Reinvestment Plan (in shares)	24,345
Dividend Reinvestment Plan	$ 1	845	0	0	0	846
Restricted stock units vested (in shares)	51,552
Restricted stock units vested	$ 0	0	0	0	0	0
Shares withheld related to net share settlement of RSUs	$ 0	(707)	0	0	0	(707)
Stock issued to directors (in shares)	21,160
Stock issued to directors	$ 0	749	0	0	0	749
Stock -based compensation	0	1,525	0	0	0	1,525
Cash dividends	0	0	0	(24,754)	0	(24,754)
Total other comprehensive (loss)/income, net of tax	0	0	9,073	0	0	9,073
Net income	$ 0	0	0	72,244	0	72,244
Purchases of treasury stock (in shares)	(641,894)
Purchases of treasury stock	$ 0	0	0	0	(23,008)	(23,008)
Balance (in shares) at Jun. 30, 2019	79,818,003
Ending balance, loss, net of tax at Jun. 30, 2019	$ 900	945,250	(1,358)	1,568,351	(313,846)	2,199,297
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
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) 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)	72,568
Dividend Reinvestment Plan	$ 1	1,705	0	0	0	1,706
Restricted stock units vested (in shares)	186,887
Restricted stock units vested	$ 2	0	0	0	0	2
Shares withheld related to net share settlement of RSUs	$ 0	(1,899)	0	0	0	(1,899)
Stock issued to directors (in shares)	31,110
Stock issued to directors	$ 0	800	0	0	0	800
Stock -based compensation	0	2,544	0	0	0	2,544
Cash dividends	0	0	0	(49,332)	0	(49,332)
Total other comprehensive (loss)/income, net of tax	0	0	6,051	0	0	6,051
Net income	$ 0	0	0	101,173	0	101,173
Purchases of treasury stock (in shares)	(400,000)
Purchases of treasury stock	$ 0	0	0	0	(12,880)	(12,880)
Balance (in shares) at Jun. 30, 2020	79,619,984
Ending balance, loss, net of tax at Jun. 30, 2020	$ 903	953,616	8,353	1,710,994	(331,418)	2,342,448
Balance (in shares) at Mar. 31, 2020	79,420,267
Beginning balance, loss, net of tax at Mar. 31, 2020	$ 902	952,331	9,877	1,681,345	(331,418)	2,313,037
Dividend Reinvestment Plan (in shares)	32,903
Dividend Reinvestment Plan	$ 0	860	0	0	0	860
Restricted stock units vested (in shares)	135,704
Restricted stock units vested	$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs	$ 0	(1,376)	0	0	0	(1,376)
Stock issued to directors (in shares)	31,110
Stock issued to directors	$ 0	800	0	0	0	800
Stock -based compensation	0	1,001	0	0	0	1,001
Cash dividends	0	0	0	(24,672)	0	(24,672)
Total other comprehensive (loss)/income, net of tax	0	0	(1,524)	0	0	(1,524)
Net income	$ 0	0	0	54,321	0	54,321
Balance (in shares) at Jun. 30, 2020	79,619,984
Ending balance, loss, net of tax at Jun. 30, 2020	$ 903	$ 953,616	$ 8,353	$ 1,710,994	$ (331,418)	$ 2,342,448