Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Beginning stock options outstanding (in shares)	2,349,446	2,149,900	2,056,898
Granted (in shares)	425,204	587,862	143,862
Exercised (in shares)	(229,551)	(13,850)	(3,970)
Forfeited (in shares)	(633,978)	(374,466)	(46,890)
Ending stock options outstanding (in shares)	1,911,121	2,349,446	2,149,900
Weighted Average Exercise Price Per Share
Beginning stock options outstanding (in dollars per share)	$ 8.39	$ 9.56	$ 9.86
Granted (in dollars per share)	7.22	4.98	5.82
Exercised (in dollars per share)	5.75	4.86	6.00
Forfeited (in dollars per share)	10.36	9.89	11.72
Ending stock options outstanding (in dollars per share)	$ 7.79	$ 8.39	$ 9.56
Vested and expected to vest at December 31, 2017
Number of Shares	2,024,130
Weighted Average Exercise Price Per Share (in dollars per share)	$ 7.69
Weighted Average Contractual Life	5 years 3 months 4 days
Aggregate Intrinsic Value	$ 2,872
December 31, 2017
Number of Shares	1,462,481
Weighted Average Exercise Price Per Share (in dollars per share)	$ 8.18
Weighted Average Contractual Life	3 years 9 months 26 days
Aggregate Intrinsic Value	$ 2,054