Borrowings (Details) - Loan Agreement - CRG - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 22, 2015
Borrowings
Total borrowing capacity	$ 50,000,000
Initial amount borrowed	30,000,000
Additional borrowing capacity	10,000,000
Additional borrowing capacity if revenue milestones are achieved	$ 10,000,000
Period for interest-only payments	4 years
Period for equal quarterly installments of interest and principal	2 years
Fixed interest rate (as a percent)	12.50%
Interest rate, cash payment if electing PIK for the remaining amount (as a percent)	8.50%
Interest rate, eligible for payment-in-kind (as a percent)	4.00%
Beginning prepayment premium (as a percent)	5.00%
Annual decline in prepayment premium (as a percent)	1.00%
Prepayment premium after fifth year of loan (as a percent)	0.00%
Financing fee on each borrowing date (as a percent)	1.50%
Final facility fee (as a percent)	7.00%
Minimum cash and certain cash equivalents required to be maintained	$ 5,000,000
Target minimum revenue in 2015	7,000,000
Target minimum revenue in 2020 and in each year thereafter	$ 70,000,000
Revenue shortfall multiplier for cure right if minimum revenue targets are not achieved	2.0
First tranche, borrowed on September 22, 2015
Borrowings
Initial amount borrowed		$ 30,000,000