Summary of Significant Accounting Policies - Net Loss per Share (Details) - shares	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									2,846,668	2,548,320	15,081,949
Weighted Average Number of Shares Outstanding, Basic and Diluted	26,316,550	26,259,216	25,584,147	23,393,448	23,374,734	22,012,743	2,553,146	2,394,470	25,406,845	12,696,414	1,980,286
Convertible Preferred Stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders											12,598,370
Employee Stock options
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									2,846,668	2,543,435	2,226,698
Restricted stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders										4,885	256,881