Summary of Significant Accounting Policies - Net Loss per Share (Details) - shares	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									2,548,320	15,081,949	14,523,988
Weighted-average number of common shares used in net loss per share applicable to common stockholders - basic and diluted	23,374,734	22,012,743	2,553,146	2,394,470	2,320,781	2,150,274	1,761,457	1,682,690	12,696,414	1,980,286	1,525,018
Convertible Preferred Stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders										12,598,370	12,598,370
Stock options
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									2,543,435	2,226,698	1,330,077
Restricted stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									4,885	256,881	595,541