Stock-based Compensation Plans and Awards - Stock Options Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock option activity
Outstanding beginning balance (in shares)	2,856
Options granted (in shares)	37
Options exercised (in shares)	(413)
Options forfeited or canceled (in shares)	(340)
Outstanding ending balance (in shares)	2,140	2,856
Exercisable (in shares)	1,650
Vested and expected to vest (in shares)	2,125
Weighted average exercise price
Outstanding beginning balance (in dollars per share)	$ 8.31
Options granted (in dollars per share)	7.90
Options exercised (in dollars per share)	5.79
Options forfeited or canceled (in dollars per share)	6.39
Outstanding ending balance (in dollars per share)	9.09	$ 8.31
Exercisable (in dollars per share)	9.40
Vested and expected to vest (in dollars per share)	$ 9.12
Weighted average remaining contractual term (in years)
Options outstanding	6 years 11 months 12 days	7 years 10 months 17 days
Exercisable	6 years 9 months 11 days
Vested and expected to vest	6 years 11 months 9 days
Aggregate intrinsic value
Options outstanding (in dollars)	$ 4,443	$ 1,489
Exercisable (in dollars)	3,109
Vested and expected to vest (in dollars)	$ 4,370