Summary of Significant Accounting Policies (Effect of New Financial Accounting Standards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit related to share-based payment awards	$ 1,200
Increase to net cash from operating activities	(155,930)	$ (148,525)	$ (102,162)
Decrease to net cash from financing activities	(145,949)	(255,455)	151,754
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to net cash from operating activities		374	676
Decrease to net cash from financing activities		$ 374	$ 676
Retained Earnings | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act, cumulative-effect adjustment	4,500
AOCI | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Act, cumulative-effect adjustment	$ (4,500)