Debt - Senior Secured Debt (Details) - USD ($)									3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 28, 2017	Feb. 14, 2017	Feb. 09, 2017	Feb. 08, 2017	May 23, 2013	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Capitalized debt issuance costs	$ 150,000								$ 150,000		$ 150,000		$ 104,000
Noncash interest expense											$ 1,871,000	$ 3,071,000
Capital Royalty Partners
Debt Instrument [Line Items]
Original debt amount converted	$ 22,700,000
Converted debt from CRG | Preferred Stock | Series A Preferred Stock
Debt Instrument [Line Items]
Number of shares issued upon conversion of debt				2,500,000							2,500,000
Convertible preferred stock, shares issuable upon conversion	125,000								125,000		125,000
Converted debt from CRG | Preferred Stock | Series B Preferred Stock
Debt Instrument [Line Items]
Convertible preferred stock, shares issuable upon conversion	15,575,586								15,575,586		15,575,586
Term Loan | Converted debt from CRG
Debt Instrument [Line Items]
Original debt amount converted				$ 25,000,000	$ 25,000,000
Term Loan | Converted debt from CRG and WCAS
Debt Instrument [Line Items]
Original debt amount converted	$ 25,000,000				$ 27,500,000
Conversion price (usd per share)				$ 10
Senior Subordinated Notes
Debt Instrument [Line Items]
Noncash interest expense									$ 0	$ 100,000	$ 300,000	300,000
Senior Subordinated Notes | Converted debt from CRG
Debt Instrument [Line Items]
Share price (usd per share)	$ 1.46								$ 1.46		$ 1.46
Extinguishment of debt issuance costs	$ 100,000
Capitalized debt issuance costs	$ 100,000								$ 100,000		$ 100,000
CRG Term Loan
Debt Instrument [Line Items]
Total potential borrowings								$ 50,000,000
Debt instrument term								6 years
CRG Term Loan
Debt Instrument [Line Items]
Cash and cash equivalents covenant held						$ 2,000,000.0	$ 5,000,000.0
Interest expense									800,000	0	1,500,000	0
Noncash interest expense									$ 300,000	$ 1,000,000	$ 1,600,000	$ 2,800,000
CRG Term Loan | Term Loan | Restructured debt
Debt Instrument [Line Items]
Debt interest rate, stated percentage	13.00%					11.00%			13.00%		13.00%
Quarterly cash interest payment percent			8.00%
Threshold for change of control	30.00%	50.00%