Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options
Beginning Balance (In Shares)	1,407
Granted (In Shares)	518	634	338
Exercised (In Shares)	(184)
Forfeited/expired (In Shares)	(89)
Ending Balance (In Shares)	1,652	1,407
Expected to Vest (In Shares)	894
Exercisable (In Shares)	665
Weighted Average Exercise Price
Beginning Balance (in dollars per share)	$ 24.21
Granted (in dollars per share)	27.18
Exercised (in dollars per share)	18.83
Forfeited/expired (in dollars per share)	27.52
Ending Balance (in dollars per share)	25.56	$ 24.21
Expected to Vest (in dollars per share)	25.65
Exercisable (in dollars per share)	$ 25.39
Weighted Average Remaining Contractual Term (in Years)
Outstanding	7 years 8 months 9 days
Expected to Vest	8 years 6 months 22 days
Exercisable	6 years 4 months 10 days
Aggregate Intrinsic Value
Outstanding	$ 23,607
Expected	12,694
Exercisable	$ 9,616
Weighted Average Fair Value
Outstanding (in dollars per share)	$ 8.12
Expected to Vest (in dollars per share)	7.95
Exercisable (in dollars per share)	$ 8.35