Income Taxes (Provision for Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S. Federal:
Current									$ 46,836	$ 95,598	$ 115,557
Deferred									(48,449)	(1,559)	19,941
U.S. Federal: Total									(1,613)	94,039	135,498
U.S. State and Local:
Current									461	9,409	11,243
Deferred									15,460	4,757	16,094
U.S. State and Local: Total									15,921	14,166	27,337
International:
Current									(1,766)	22,872	22,794
Deferred									9,107	742	4,149
International: Total									7,341	23,614	26,943
Total current									45,531	127,879	149,594
Total deferred									(23,882)	3,940	40,184
Total provision for income taxes	$ (32,326)	$ 17,607	$ 4,952	$ 31,416	$ 38,204	$ 23,197	$ 33,394	$ 37,024	$ 21,649	$ 131,819	$ 189,778
Effective tax rate									7.70%	53.50%	31.10%