Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share

The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented:

	Year Ended December 31,
	2017		2016		2015
Series A convertible preferred shares/stock		—		611,392		2,172,520
Series B convertible preferred stock		—		1,407,097		4,047,734
Unvested restricted common stock		57,629		100,634		153,355
Options to purchase common stock		2,043,420		1,063,778		450,458