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	120,468	0	0	0	120,468	0
Foreign currency translation adjustment	(24)	0	0	0	0	(24)
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	225	$ 0	$ 0	0	0	225
Stock based compensation, shares		86	25
Stock based compensation, value	1,929	$ 0	$ (1,646)	3,575	0	0
Issuance of shares		21
Issuance of shares, treasury stock			(38)
Issuance of shares, value	2,660	$ 1	$ 1,014	1,645	0	0
Dividends on common stock	$ (57,562)	0	0	0	(57,562)	0
Dividends per share	$ 1.15
Balance, end of period at Jun. 30, 2019	$ 2,010,078	$ 540	$ (96,178)	1,504,290	611,159	(9,733)
Balance, shares at Jun. 30, 2019		53,996	3,553
Balance, shares at Mar. 31, 2019		53,996	3,556
Balance, beginning of period at Mar. 31, 2019	1,989,792	$ 540	$ (96,260)	1,502,993	592,278	(9,759)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	47,662	0	0	0	47,662	0
Foreign currency translation adjustment	(87)	0	0	0	0	(87)
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	1,169	$ 0	$ 0	1,169	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(3)
Issuance of shares, value	210	$ 0	$ 82	128	0	0
Dividends on common stock	$ (28,781)	0	0	0	(28,781)	0
Dividends per share	$ 0.575
Balance, end of period at Jun. 30, 2019	$ 2,010,078	$ 540	$ (96,178)	1,504,290	611,159	(9,733)
Balance, shares at Jun. 30, 2019		53,996	3,553
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	72,198	0	0	0	72,198	0
Foreign currency translation adjustment	93	0	0	0	0	93
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	226	$ 0	$ 0	0	0	226
Stock based compensation, shares		146	35
Stock based compensation, value	1,430	$ 0	$ (2,740)	4,170	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(11)
Issuance of shares, value	687	$ 0	$ 317	370	0	0
Dividends on common stock	$ (60,172)	0	0	0	(60,172)	0
Dividends per share	$ 1.20
Balance, end of period at Jun. 30, 2020	$ 2,053,556	$ 541	$ (98,438)	1,513,510	647,272	(9,329)
Balance, shares at Jun. 30, 2020		54,145	3,571
Balance, shares at Mar. 31, 2020		54,145	3,578
Balance, beginning of period at Mar. 31, 2020	2,060,476	$ 541	$ (98,644)	1,512,148	655,865	(9,434)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	21,494	0	0	0	21,494	0
Foreign currency translation adjustment	(8)	0	0	0	0	(8)
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	1,139	$ 0	$ 0	1,139	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(7)
Issuance of shares, value	429	$ 0	$ 206	223	0	0
Dividends on common stock	$ (30,087)	0	0	0	(30,087)	0
Dividends per share	$ 0.600
Balance, end of period at Jun. 30, 2020	$ 2,053,556	$ 541	$ (98,438)	$ 1,513,510	$ 647,272	$ (9,329)
Balance, shares at Jun. 30, 2020		54,145	3,571