Credit Facility and Term Loans - Additional Information (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 23, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Oct. 16, 2017
Debt Instrument [Line Items]
Available balance of credit facility		$ 800,000		$ 800,000		$ 1,400,000	$ 5,600,000
Interest expense		955,000	$ 439,000	3,456,000	$ 1,503,000
Repaying of term loan					1,344,000
Borrowings, outstanding		27,000,000		27,000,000		27,500,000	$ 10,300,000
Term Loan
Debt Instrument [Line Items]
Credit facility maximum borrowing amount						$ 15,000,000
Interest expense		500,000		1,500,000
Amortization of debt issuance costs		100,000
Debt instrument maturity month and year						2023-01
Borrowings, outstanding		15,000,000		15,000,000
Horizon Term Loan
Debt Instrument [Line Items]
Debt offset against and expense over the term						5 years
Repaying of term loan						$ 4,900,000
Warrants term						10 years
Fair value on issuance						$ 900,000
Debt discount						900,000
Deferred debt issuance costs		906,000		906,000		$ 1,022,000
Horizon Term Loan | Common Stock
Debt Instrument [Line Items]
Warrants to purchase shares						76,923
Warrants to purchase shares, exercise price						$ 15.60
Maximum | Term Loan
Debt Instrument [Line Items]
Amortization of debt issuance costs				$ 400,000
Mid Cap Prior Term Loan
Debt Instrument [Line Items]
Term loan, borrowing								$ 7,000,000
Interest expense			200,000		700,000
Repaying of term loan						$ 4,900,000
Prepayment penalty						$ 100,000
Mid Cap Prior Term Loan | Maximum
Debt Instrument [Line Items]
Amortization of debt issuance costs			100,000		100,000
London Interbank Offered Rate (LIBOR) | Term Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate						9.90%
Description of variable rate basis				one-month LIBOR
London Interbank Offered Rate (LIBOR) | Minimum [Member] | Term Loan
Debt Instrument [Line Items]
Potential additional interest						2.50%
Mid Cap Prior Credit Facility
Debt Instrument [Line Items]
Credit facility maximum borrowing amount								$ 15,000,000
Unamortized debt issuance costs						$ 700,000
Mid Cap Credit Facility
Debt Instrument [Line Items]
Credit facility maximum borrowing amount	$ 25,000,000
Additional increase in borrowing amount	$ 50,000,000
Line of credit facility, unused capacity, commitment fee percentage	0.50%
Line of credit facility, minimum liquidity financial covenant requirement in cash on hand	$ 5,000,000
Debt issuance costs						$ 1,300,000
Debt offset against and expense over the term						3 years
Line of credit, outstanding		15,100,000		$ 15,100,000		$ 16,500,000
Available balance of credit facility		800,000		800,000		1,400,000
Current borrowing capacity						25,000,000
Mid Cap Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	5.75%
Revolving Credit Facility
Debt Instrument [Line Items]
Interest expense		400,000	200,000	1,900,000	800,000
Amortization of debt issuance costs		$ 200,000	$ 100,000	$ 500,000	$ 300,000
Credit Facility and Term Loan
Debt Instrument [Line Items]
Line of credit facility covenant minimum liquidity requirement in unrestricted cash						$ 5,000,000