Fair Value Measurements - Warrants and other (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2015	Feb. 28, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2006
Fair Value Measurements, Valuation
Fair value adjustment of warrants			$ 1,132,000	$ (5,000)	$ (271,000)
Common shares issued, net settlement of warrants exercised (in shares)			44,914
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
Fair value adjustment of warrants			$ (900,000)	$ (5,000)	(300,000)
Common Stock Warrants | Amended Agreement
Fair Value Measurements, Valuation
Shares that may be purchased under warrant (in shares)		11,298
Exercise price of warrants (in dollars per share)		$ 8.85
Fair value adjustment of warrants			200,000
Stock warrant liabilities, fair value		$ 53,000	$ 100,000
Warrants exercised (in shares)	5,649
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
Fair value adjustment of warrants			$ 0	$ 0	$ (100,000)
IPO
Fair Value Assumptions
Share price (in dollars per share)			$ 18.00