Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($)	Common Stock Outstanding [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Beginning balance, loss, net of tax at Dec. 31, 2018	$ 898,000	$ 942,062,000	$ (18,006,000)	$ 1,479,149,000	$ (282,237,000)	$ 2,121,866,000
Dividend Reinvestment Plan (in shares)	22,945
Dividend Reinvestment Plan	$ 0	835,000	0	0	0	835,000
Restricted stock units vested (in shares)	71,647
Restricted stock units vested	$ 1,000	0	0	0	0	1,000
Shares withheld related to net share settlement of RSUs	$ 0	(1,593)	0	0	0	(1,593)
Purchases of treasury stock (in shares)	(233,700)
Purchases of treasury stock	$ 0	0	0	0	(8,601,000)	(8,601,000)
Stock -based compensation	0	1,534,000	0	0	0	1,534,000
Cash dividends	0	0	0	(24,967,000)	0	(24,967,000)
Total other comprehensive (loss)/income, net of tax	0	0	7,575,000	0	0	7,575,000
Net income	0	0	0	66,679,000	0	66,679,000
Ending balance, loss, net of tax at Mar. 31, 2019	$ 899,000	942,838,000	(10,431,000)	1,520,861,000	(290,838,000)	2,163,329,000
Balance (in shares) at Dec. 31, 2018	80,501,948
Change in other comprehensive loss	$ 0	0	7,575,000	0	0	7,575,000
Balance (in shares) at Mar. 31, 2019	80,362,840
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)	39,665
Dividend Reinvestment Plan	$ 1,000	845,000	0	0	0	846,000
Restricted stock units vested (in shares)	51,183
Restricted stock units vested	$ 1,000	0	0	0	0	1,000
Shares withheld related to net share settlement of RSUs	$ 0	(523,000)	0	0	0	(523,000)
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	1,543,000	0	0	0	1,543,000
Cash dividends	0	0	0	(24,660,000)	0	(24,660,000)
Total other comprehensive (loss)/income, net of tax	0	0	7,575,000	0	0	7,575,000
Net income	$ 0	0	0	46,852,000	0	46,852,000
Balance (in shares) at Mar. 31, 2020	79,420,267
Ending 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
Change in other comprehensive loss	$ 0	$ 0	$ 7,575,000	$ 0	$ 0	$ 7,575,000