Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	(400,000)	(22,000)	(500,000)
Forfeited (in Shares)			(298,000)
Options outstanding, ending balance (in Shares)	3,733,000		3,733,000		4,053,000
Options, exercisable (in Shares)	2,164,000		2,164,000
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)			24.76
Weighted average exercise price, ending balance (in Dollars per share)	$ 29.30		29.30		$ 28.95
Weighted average exercise price, exercisable (in Dollars per share)	$ 30.08		$ 30.08
Weighted Average Remaining Contractual Term			4 years 15 days		4 years 6 months 22 days
Weighted Average Remaining Contractual Term, exercisable			3 years 5 months 10 days
Aggregate Intrinsic Value	$ 0		$ 0		$ 21,459
Aggregate Intrinsic Value, exercisable	$ 0		$ 0