Fair Value Measurements - Warrants and other (Details) - USD ($)	1 Months Ended			12 Months Ended
	Feb. 29, 2016	Sep. 30, 2015	Feb. 28, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2010	Dec. 31, 2006
Fair Value Measurements, Valuation
Change in fair value of stock warrant liability				$ 43,000	$ (1,132,000)	$ 5,000
Common shares issued, net settlement of warrants exercised (in shares)				44,914
Amount of transfers of assets and liabilities measured on a recurring basis between Levels 1, 2 and 3 of the fair value hierarchy				$ 0	0	0
Amended Agreement
Fair Value Measurements, Valuation
Change in fair value of stock warrant liability				43,000	(200,000)	0
Common Stock Warrants | Amended Agreement
Fair Value Measurements, Valuation
Shares that may be purchased under warrant (in shares)	5,649		11,298
Exercise price of warrants (in dollars per share)			$ 8.85
Stock warrant liabilities, fair value			$ 53,000		100,000
Warrants exercised (in shares)	5,649	5,649
Change in fair value of stock warrant liability					$ (200,000)
Common shares issued, net settlement of warrants exercised (in shares)		5,649			5,649
Fair Value Assumptions
Risk free interest rate (as a percent)			1.90%		1.90%
Dividend yield (as a percent)			0.00%		0.00%
Expected volatility rate (as a percent)			70.00%		54.80%
Expected life			7 years		6 years 2 months 12 days
Warrants To Purchase Shares Of Series C Convertible Preferred Stock Member
Fair Value Measurements, Valuation
Shares that may be purchased under warrant (in shares)								185,714
Exercise price of warrants (in dollars per share)								$ 7.00
Change in fair value of stock warrant liability				$ 0	$ 0	$ 0
Warrants to Purchase Shares of Series D Convertible Preferred Stock
Fair Value Measurements, Valuation
Shares that may be purchased under warrant (in shares)							156,860
Exercise price of warrants (in dollars per share)							$ 7.65
Warrants exercised (in shares)					127,526	29,334
Warrants exercised, settled in cash (in shares)				49,410
Warrants exercised, net settlement (in shares)				78,116
Warrants to Purchase Shares of Series D Convertible Preferred Stock | Amended Agreement
Fair Value Measurements, Valuation
Change in fair value of stock warrant liability				$ 0	$ (900,000)	$ 5,000
IPO
Fair Value Assumptions
Share price (in dollars per share)				$ 18.00