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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 190,149	$ 198,719	$ 236,103	$ 76,472	$ 163,127	$ 83,534	$ 130,391	$ 125,114	$ 701,443	$ 502,166	$ 684,047
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted Average Number of Shares Outstanding, Basic									64,274	66,553	69,248
Equivalent shares from outstanding stock options									715	739	714
Weighted Average Number of Shares Outstanding, Diluted									64,989	67,292	69,962
Earnings per share
Earnings Per Share, Basic (in dollars per share)	$ 2.96	$ 3.10	$ 3.68	$ 1.18	$ 2.49	$ 1.26	$ 1.97	$ 1.84	$ 10.91	$ 7.55	$ 9.88
Earnings Per Share, Diluted (in dollars per share)	$ 2.92	$ 3.07	$ 3.64	$ 1.17	$ 2.46	$ 1.25	$ 1.94	$ 1.81	$ 10.79	$ 7.46	$ 9.78