Earnings Per Share (Schedule of Earnings Per Share Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 163,127	$ 83,534	$ 130,391	$ 125,114	$ 191,091	$ 157,996	$ 198,296	$ 136,664	$ 502,166	$ 684,047	$ 418,837
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted Average Number of Shares Outstanding, Basic									66,553	69,248	71,917
Equivalent shares from outstanding stock options									739	714	544
Weighted Average Number of Shares Outstanding, Diluted									67,292	69,962	72,461
Earnings per share
Earnings Per Share, Basic (in dollars per share)	$ 2.49	$ 1.26	$ 1.97	$ 1.84	$ 2.78	$ 2.30	$ 2.87	$ 1.94	$ 7.55	$ 9.88	$ 5.82
Earnings Per Share, Diluted (in dollars per share)	$ 2.46	$ 1.25	$ 1.94	$ 1.81	$ 2.75	$ 2.28	$ 2.84	$ 1.92	$ 7.46	$ 9.78	$ 5.78