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, 2017		52,981		3,609
Balance, beginning of period at Dec. 31, 2017	$ 1,798,915	$ 530	$ 1,445,181	$ (96,376)	$ 458,352	$ (8,772)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	102,286	0	0	0	102,286	0
Foreign currency translation adjustment	181	0	0	0	0	181
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		72		(35)
Stock based compensation, value	5,511	$ 0	4,903	$ 608	0	0
Issuance of shares		836
Issuance of shares, treasury stock				0
Issuance of shares, value	44,865	$ 9	44,856	$ 0	0	0
Dividends on common stock	$ (54,253)	0	0	0	(54,253)	0
Dividends per share	$ 1.100
Balance, end of period at Jun. 30, 2018	$ 1,897,731	$ 539	1,494,940	$ (95,768)	508,528	(10,508)
Balance, shares at Jun. 30, 2018		53,889		3,574
Balance, shares at Mar. 31, 2018		53,052		3,579
Balance, beginning of period at Mar. 31, 2018	1,834,623	$ 531	1,448,622	$ (95,872)	492,049	(10,707)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	43,787	0	0	0	43,787	0
Foreign currency translation adjustment	86	0	0	0	0	86
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		1		0
Stock based compensation, value	1,289	$ 0	1,232	$ 57	0	0
Issuance of shares		836
Issuance of shares, treasury stock				(5)
Issuance of shares, value	45,141	$ 8	45,086	$ 47	0	0
Dividends on common stock	$ (27,308)	0	0	0	(27,308)	0
Dividends per share	$ 0.550
Balance, end of period at Jun. 30, 2018	$ 1,897,731	$ 539	1,494,940	$ (95,768)	508,528	(10,508)
Balance, shares at Jun. 30, 2018		53,889		3,574
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of certain tax effects from AOCL	0	$ 0	0	$ 0	2,143	(2,143)
Balance, shares at Dec. 31, 2018		53,889		3,566
Balance, beginning of period at Dec. 31, 2018	1,942,382	$ 539	1,499,070	$ (95,546)	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	3,575	$ (1,646)	0	0
Issuance of shares		21
Issuance of shares, treasury stock				(38)
Issuance of shares, value	2,660	$ 1	1,645	$ 1,014	0	0
Dividends on common stock	$ (57,562)	0	0	0	(57,562)	0
Dividends per share	$ 1.150
Balance, end of period at Jun. 30, 2019	$ 2,010,078	$ 540	1,504,290	$ (96,178)	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	1,502,993	$ (96,260)	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	1,169	$ 0	0	0
Issuance of shares		0
Issuance of shares, treasury stock				(3)
Issuance of shares, value	210	$ 0	128	$ 82	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	$ 1,504,290	$ (96,178)	$ 611,159	$ (9,733)
Balance, shares at Jun. 30, 2019		53,996		3,553