Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Option Activity and Outstanding Options
Options outstanding	433
Forfeited, cancelled or expired	(1)
Exercised	(135)
Options outstanding	297	433
Stock Option Activity and Weighted-Average Exercise Price
Beginning of period, Weighted Average Exercise Price (in dollars per share)	$ 5.03
Forfeited, canceled or expired, Weighted Average Exercise Price (in dollars per share)	15.58
Exercises, Weighted Average Exercise Price (in dollars per share)	4.15
End of period, Weighted Average Exercise Price (in dollars per share)	$ 5.37	$ 5.03
Options outstanding, Aggregate Intrinsic Value	$ 2,405
Options outstanding, Weighted-Average Remaining Contractual Life	2 years 1 month 6 days
Options exercisable, Number of Options Exercisable	291
Options exercisable, Weighted-Average Exercise Price	$ 5.19
Options exercisable, aggregate intrinsic value	$ 2,401
Options exercisable, Weighted average remaining contractual term	2 years
Vested and expected to vest	297
Vested and expected to vest, Weighted Average Exercise Price	$ 5.37
Vested and expected to vest, Aggregate Intrinsic Value	$ 2,405
Vested and expected to vest, remaining contractual term (in years)	2 years 1 month 6 days
General and administrative	$ 1,856	$ 2,613	$ 1,484
Weighted average grant-date fair value of stock options granted	$ 0	$ 0	$ 8.94
Stock options
Stock Option Activity and Weighted-Average Exercise Price
General and administrative	$ 84	$ 389	$ 327
Compensation expense for unvested stock options	$ 2,600
Minimum | Stock options
Stock Option Activity and Weighted-Average Exercise Price
Weighted average period for unvested stock options	4 months 24 days
Maximum | Stock options
Stock Option Activity and Weighted-Average Exercise Price
Weighted average period for unvested stock options	1 year 3 months 18 days