Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Number of Options
Options outstanding, beginning balance (in Shares)			4,053,000
Granted (in Shares)			0
Exercised (in Shares)	0	(100,000)	(22,000)	(600,000)
Forfeited (in Shares)			(518,000)
Options outstanding, ending balance (in Shares)	3,514,000		3,514,000		4,053,000
Options, exercisable (in Shares)	2,239,000		2,239,000
Weighted Average Exercise Price
Weighted average exercise price, beginning balance (in Dollars per share)			$ 28.95
Granted (in Dollars per share)			0.00
Exercised (in Dollars per share)			24.99
Forfeited (in Dollars per share)			31.76
Weighted average exercise price, ending balance (in Dollars per share)	$ 28.56		28.56		$ 28.95
Weighted average exercise price, exercisable (in Dollars per share)	$ 29.16		$ 29.16
Weighted Average Remaining Contractual Term			3 years 11 months 11 days		4 years 6 months 22 days
Weighted Average Remaining Contractual Term, exercisable			3 years 7 months 15 days
Aggregate Intrinsic Value	$ 0		$ 0		$ 21,459
Aggregate Intrinsic Value, exercisable	$ 0		$ 0