Net Loss Per Share - Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Class of Stock [Line Items]
Net loss	$ (11,525)	$ (11,029)	$ (23,570)	$ (18,476)
Weighted-average common shares outstanding - basic and diluted (in shares)	40,593,908	39,627,842	40,522,790	39,610,905
Basic and diluted net loss per share (in dollars per share)	$ (0.28)	$ (0.28)	$ (0.58)	$ (0.47)
Class A Common Stock
Class of Stock [Line Items]
Net loss	$ (8,219)	$ (7,578)	$ (16,718)	$ (12,686)
Weighted-average common shares outstanding - basic and diluted (in shares)	28,950,226	27,226,993	28,742,233	27,197,080
Basic and diluted net loss per share (in dollars per share)	$ (0.28)	$ (0.28)	$ (0.58)	$ (0.47)
Class B Common Stock
Class of Stock [Line Items]
Net loss	$ (3,306)	$ (3,451)	$ (6,852)	$ (5,790)
Weighted-average common shares outstanding - basic and diluted (in shares)	11,643,682	12,400,848	11,780,557	12,413,825
Basic and diluted net loss per share (in dollars per share)	$ (0.28)	$ (0.28)	$ (0.58)	$ (0.47)