CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, shares at Dec. 31, 2018		53,889	3,566
Balance, beginning of period at Dec. 31, 2018	$ 1,942,382	$ 539	$ (95,546)	$ 1,499,070	$ 548,253	$ (9,934)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	142,138	0	0	0	142,138	0
Foreign currency translation adjustment	18	0	0	0	0	18
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	339	$ 0	$ 0	0	0	339
Stock based compensation, shares		107	25
Stock based compensation, value	3,098	$ 0	$ (1,646)	4,744	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(41)
Issuance of shares, value	2,892	$ 1	$ 1,100	1,791	0	0
Dividends on common stock	$ (86,343)	0	0	0	(86,343)	0
Dividends per share	$ 1.725
Balance, end of period at Sep. 30, 2019	$ 2,004,524	$ 540	$ (96,092)	1,505,605	604,048	(9,577)
Balance, shares at Sep. 30, 2019		53,996	3,550
Balance, shares at Jun. 30, 2019		53,996	3,553
Balance, beginning of period at Jun. 30, 2019	2,010,078	$ 540	$ (96,178)	1,504,290	611,159	(9,733)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	21,670	0	0	0	21,670	0
Foreign currency translation adjustment	42	0	0	0	0	42
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	114	$ 0	$ 0	0	0	114
Stock based compensation, shares		0	0
Stock based compensation, value	1,169	$ 0	$ 0	1,169	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(3)
Issuance of shares, value	232	$ 0	$ 86	146	0	0
Dividends on common stock	$ (28,781)	0	0	0	(28,781)	0
Dividends per share	$ 0.575
Balance, end of period at Sep. 30, 2019	$ 2,004,524	$ 540	$ (96,092)	1,505,605	604,048	(9,577)
Balance, shares at Sep. 30, 2019		53,996	3,550
Balance, shares at Dec. 31, 2019		53,999	3,547
Balance, beginning of period at Dec. 31, 2019	2,039,094	$ 541	$ (96,015)	1,508,970	635,246	(9,648)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	101,664	0	0	0	101,664	0
Foreign currency translation adjustment	90	0	0	0	0	90
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	339	$ 0	$ 0	0	0	339
Stock based compensation, shares		146	35
Stock based compensation, value	2,570	$ 0	$ (2,740)	5,310	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(18)
Issuance of shares, value	1,053	$ 0	$ 513	540	0	0
Dividends on common stock	$ (90,260)	0	0	0	(90,260)	0
Dividends per share	$ 1.80
Balance, end of period at Sep. 30, 2020	$ 2,054,550	$ 541	$ (98,242)	1,514,820	646,650	(9,219)
Balance, shares at Sep. 30, 2020		54,145	3,564
Balance, shares at Jun. 30, 2020		54,145	3,571
Balance, beginning of period at Jun. 30, 2020	2,053,556	$ 541	$ (98,438)	1,513,510	647,272	(9,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	29,466	0	0	0	29,466	0
Foreign currency translation adjustment	(3)	0	0	0	0	(3)
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	113	$ 0	$ 0	0	0	113
Stock based compensation, shares		0	0
Stock based compensation, value	1,140	$ 0	$ 0	1,140	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(7)
Issuance of shares, value	366	$ 0	$ 196	170	0	0
Dividends on common stock	$ (30,088)	0	0	0	(30,088)	0
Dividends per share	$ 0.600
Balance, end of period at Sep. 30, 2020	$ 2,054,550	$ 541	$ (98,242)	$ 1,514,820	$ 646,650	$ (9,219)
Balance, shares at Sep. 30, 2020		54,145	3,564