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	58,499	0	0	0	58,499	0
Foreign currency translation adjustment	95	0	0	0	0	95
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		71		(30)
Stock based compensation, value	1,817	$ 1	2,485	$ (669)	0	0
Issuance of shares		0
Issuance of shares, treasury stock				0
Issuance of shares, value	2,129	$ 0	956	$ 1,173	0	0
Dividends on common stock	$ (26,945)	0	0	0	(26,945)	0
Dividends per share	$ 0.550
Balance, end of period at Mar. 31, 2018	$ 1,834,623	$ 531	1,448,622	$ (95,872)	492,049	(10,707)
Balance, shares at Mar. 31, 2018		53,052		3,579
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	72,806	0	0	0	72,806	0
Foreign currency translation adjustment	63	0	0	0	0	63
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	112	$ 0	0	$ 0	0	112
Stock based compensation, shares		86		25
Stock based compensation, value	760	$ 0	2,406	$ (1,646)	0	0
Issuance of shares		21
Issuance of shares, treasury stock				(35)
Issuance of shares, value	2,450	$ 1	1,517	$ 932	0	0
Dividends on common stock	$ (28,781)	0	0	0	(28,781)	0
Dividends per share	$ 0.575
Balance, end of period at Mar. 31, 2019	$ 1,989,792	$ 540	$ 1,502,993	$ (96,260)	$ 592,278	$ (9,759)
Balance, shares at Mar. 31, 2019		53,996		3,556