STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]
Common Stock, Dividends, Declared, Annualized Basis	$ 1.20
Shares Issued, beginning balance at Dec. 31, 2015					52,598,005
Equity, beginning balance at Dec. 31, 2015	$ 1,841,555	$ 95,046	$ (4,401)	$ (14,491)	$ 526	$ 1,764,875
Net income	140,095	140,095	0	0	0	0
Other comprehensive loss	(314)	0	(314)	0	0	0
Repurchase of common stock	(24,066)	0	0	(24,066)	$ 0	0
Common stock issued, shares					0
Common stock issued, value	4,219	0	0	20,431	$ 0	(16,212)
Common stock dividends	(73,209)	(74,120)	0	0	$ 0	911
Shares Issued, ending balance at Dec. 31, 2016					52,598,005
Equity, ending balance at Dec. 31, 2016	1,888,280	161,021	(4,715)	(18,126)	$ 526	1,749,574
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	$ (10,982)	(10,982)	0	0	0	0
Common Stock, Dividends, Declared, Annualized Basis	$ 1.40
Net income	$ 162,995	162,995	0	0	0	0
Other comprehensive loss	(778)	0	(778)	0	0	0
Repurchase of common stock	(17,512)	0	0	(17,512)	$ 0	0
Common stock issued, shares					0
Common stock issued, value	4,193	0	0	17,142	$ 0	(12,949)
Common stock dividends	(87,951)	(88,877)	0	0	$ 0	926
Shares Issued, ending balance at Dec. 31, 2017					52,598,005
Equity, ending balance at Dec. 31, 2017	$ 1,960,209	246,121	(5,493)	(18,496)	$ 526	1,737,551
Common Stock, Dividends, Declared, Annualized Basis	$ 1.68
Net income	$ 172,234	172,234	0	0	0	0
Other comprehensive loss	1,407	0	1,407	0	$ 0	0
Common stock issued, shares					0
Common stock issued, value	5,400	0	0	16,351	$ 0	(10,951)
Common stock dividends	(96,594)	(97,486)	0	0	$ 0	892
Shares Issued, ending balance at Dec. 31, 2018					52,598,005
Equity, ending balance at Dec. 31, 2018	$ 2,042,656	$ 320,869	$ (4,086)	$ (2,145)	$ 526	$ 1,727,492