Weighted Average Shares Outstanding and Net Loss Per Share - Summary of Reconciliation of Weighted Average Shares Outstanding Used in Calculating Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net loss allocated to common shareholders for basic calculation	$ (11,423)	$ (23,790)
Weighted average common shares outstanding, basic	39,908	39,649
Weighted average common shares outstanding, diluted	39,908	39,649
Net loss per share, basic	$ (0.29)	$ (0.60)
Net loss per share, diluted	$ (0.29)	$ (0.60)