Net Loss Per Share - Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Class of Stock [Line Items]
Net loss	$ (12,891)	$ (14,630)	$ (36,461)	$ (33,106)
Weighted-average common shares outstanding - basic and diluted (in shares)	40,762,960	39,980,308	40,603,430	39,735,393
Basic and diluted net loss per share (in dollars per share)	$ (0.32)	$ (0.37)	$ (0.90)	$ (0.83)
Class A Common Stock
Class of Stock [Line Items]
Net loss	$ (9,369)	$ (10,199)	$ (26,076)	$ (22,849)
Weighted-average common shares outstanding - basic and diluted (in shares)	29,624,794	27,870,414	29,038,566	27,423,991
Basic and diluted net loss per share (in dollars per share)	$ (0.32)	$ (0.37)	$ (0.90)	$ (0.83)
Class B Common Stock
Class of Stock [Line Items]
Net loss	$ (3,522)	$ (4,431)	$ (10,385)	$ (10,257)
Weighted-average common shares outstanding - basic and diluted (in shares)	11,138,166	12,109,894	11,564,864	12,311,402
Basic and diluted net loss per share (in dollars per share)	$ (0.32)	$ (0.37)	$ (0.90)	$ (0.83)