Net Loss Per Share - Weighted-Average Anti-Dilutive Securities Not Included in Diluted Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in diluted net loss per share (in shares)	665	1,681	668	1,700
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in diluted net loss per share (in shares)	594	655	611	669
Unvested restricted share awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in diluted net loss per share (in shares)	63	64	49	69
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in diluted net loss per share (in shares)	8	962	8	962