Stock-Based Compensation - Summary of restricted stock unit activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Market-based RSUs
Number of RSUs
Outstanding at the beginning of the period (in shares)	625,308
Canceled due to modification of award (in shares)	(501,129)
Granted (in shares)	0
Canceled due to non-achievement of performance or market condition (in shares)	(53,754)
Outstanding at the end of the period (in shares)	70,425	625,308
RSUs expected to be converted into shares of Common stock (in shares)	0
Weighted-Average Grant-Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 13.65
Canceled due to modification of award (in dollars per share)	13.11
Granted (in dollars per share)		$ 13.01	$ 18.67
Canceled due to non-achievement of performance or market condition (in dollars per share)	18.67
Outstanding at the end of the period (in dollars per share)	13.67	$ 13.65
RSUs expected to be converted into shares of Common stock (in dollars per share)	$ 13.67
Service-based RSUs
Number of RSUs
Outstanding at the beginning of the period (in shares)	885,117
Canceled due to modification of award (in shares)	(489,561)
Granted (in shares)	56,958
Converted (in shares)	(268,282)
Outstanding at the end of the period (in shares)	184,232	885,117
RSUs expected to be converted into shares of Common stock (in shares)	184,232
Weighted-Average Grant-Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 15.48
Canceled due to modification of award (in dollars per share)	14.24
Granted (in dollars per share)	14.07
Converted (in dollars per share)	17.95
Outstanding at the end of the period (in dollars per share)	16.02	$ 15.48
RSUs expected to be converted into shares of Common stock (in dollars per share)	$ 16.02