Shareholders Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]
Common Stock, Shares, Outstanding		145,871
Stockholders' Equity Attributable to Parent at Dec. 31, 2014	$ 2,113,745	$ 14,587	$ 405,982	$ (75,025)	$ 1,768,201
Common Stock Issued to Directors	500,000	2,000	498,000
Dividends, Cash	$ (64,108)				(64,108)
Net Income (Loss) Attributable to Parent	243,318				243,318
Stock Issued During Period, Value, Employee Benefit Plan		528
Stock Issued During Period, Value, Employee Benefit Plan	28,045	$ 53	$ 27,992
Treasury Stock, Value, Acquired, Cost Method	(175,000)		(11,250)	(163,750)
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	3,276		3,276
Common Stock Issued to Directors Shares		16
Stockholders' Equity Attributable to Parent at Dec. 31, 2015	$ 2,149,776	$ 14,642	$ 426,498	(238,775)	1,947,411
Common Stock, Shares, Outstanding		146,415
Common Stock Issued to Directors	500,000	2,000	498,000
Dividends, Cash	$ (70,262)				(70,262)
Net Income (Loss) Attributable to Parent	257,491				257,491
Stock Issued During Period, Value, Employee Benefit Plan		1,675
Stock Issued During Period, Value, Employee Benefit Plan	23,018	$ 167	$ 22,851
Treasury Stock, Value, Acquired, Cost Method	(7,658)		11,250	(18,908)
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	7,346		7,346
Common Stock Issued to Directors Shares		17
Stockholders' Equity Attributable to Parent at Dec. 31, 2016	$ 2,360,211	$ 14,811	$ 468,443	(257,683)	2,134,640
Common Stock, Shares, Outstanding	140,103,841	148,107
Net Unrealized Holding Gain on Available for Sale Securities	$ (12)
Common Stock Issued to Directors	500,000	1,000	499,000
Dividends, Cash	$ (77,712)				(77,712)
Net Income (Loss) Attributable to Parent	399,630				399,630
Stock Issued During Period, Value, Employee Benefit Plan		706
Stock Issued During Period, Value, Employee Benefit Plan	39,965	$ 70	$ 39,895
Treasury Stock, Value, Acquired, Cost Method	(139,889)		(11,250)	(128,639)
Common Stock Issued to Directors Shares		11
Stockholders' Equity Attributable to Parent at Dec. 31, 2017	$ 2,582,699	$ 14,882	497,540	$ (386,322)	2,456,599
Common Stock, Shares, Outstanding	138,105,455	148,824
Net Unrealized Holding Gain on Available for Sale Securities	$ (6)		$ (47)		$ 41