Stockholders' Equity (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 21, 2015	Oct. 17, 2014	Oct. 21, 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments for Repurchase of Common Stock	$ 42,938	$ 120,309	$ 93,218
Remaining Number of Shares Authorized to be Repurchased	1,300,000
Shares Paid for Tax Withholding for Share Based Compensation	105,000	85,000	82,000
Payments related to tax withholding for share based compensation (in USD)	$ 4,700	$ 2,600	$ 2,600
Repurchase plan authorized in Oct 2008 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)						6,000,000
Stock Repurchased and Retired During Period, Shares			2,800,000
Payments for Repurchase of Common Stock			$ 90,600
Repurchase plan authorized in Oct 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)					3,000,000
Stock Repurchased and Retired During Period, Shares		3,800,000
Payments for Repurchase of Common Stock		$ 117,700
Repurchase plan approved in Oct 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)				3,000,000
Stock Repurchased and Retired During Period, Shares	900,000
Payments for Repurchase of Common Stock	$ 38,300