CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, shares at Dec. 31, 2015		51,789		3,617
Balance, beginning of period at Dec. 31, 2015	$ 1,600,174	$ 518	$ 1,376,291	$ (93,948)	$ 325,909	$ (8,596)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	120,041	0	0	0	120,041	0
Foreign currency translation adjustment	(84)	0	0	0	0	(84)
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	(1,432)	$ 0	0	$ 0	0	(1,432)
Stock based compensation, shares		168		13
Stock based compensation, value	3,746	$ 0	5,650	$ (1,904)	0	0
Issuance of shares		0
Issuance of shares, value	(9)	$ 2		$ 0	0	0
Adjustments to additional paid in capital, stock issued, issuance costs			(11)
Issuance of shares, treasury stock				0
Dividends on common stock	$ (71,816)	0	0	$ 0	(71,816)	0
Dividends per share	$ 1.50
Balance, end of period at Sep. 30, 2016	$ 1,653,223	$ 520	1,381,930	$ (95,852)	376,737	(10,112)
Balance, shares at Sep. 30, 2016		51,957		3,630
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting standard adoption, cumulative-effect adjustment to retained earnings	2,603	$ 0	0	$ 0	2,603	0
Balance, shares at Dec. 31, 2016		51,958		3,626
Balance, beginning of period at Dec. 31, 2016	1,676,227	$ 520	1,384,271	$ (95,769)	396,919	(9,714)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	114,809	0	0	0	114,809	0
Foreign currency translation adjustment	(197)	0	0	0	0	(197)
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	278	$ 0	0	$ 0	0	278
Stock based compensation, shares		134		(14)
Stock based compensation, value	5,897	$ 2	6,588	$ (693)	0	0
Issuance of shares		84
Issuance of shares, value	4,807	$ 0	4,807		0	0
Issuance of shares, treasury stock				0
Dividends on common stock	$ (75,633)	0	0	$ 0	(75,633)	0
Dividends per share	$ 1.575
Balance, end of period at Sep. 30, 2017	$ 1,726,188	$ 522	$ 1,395,666	$ (96,462)	$ 436,095	$ (9,633)
Balance, shares at Sep. 30, 2017		52,176		3,612