Credit Facility and Term Loans - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 23, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Oct. 16, 2017
Debt Instrument [Line Items]
Available balance of credit facility		$ 1,100,000		$ 1,100,000		$ 1,400,000	$ 5,600,000
Interest expense		1,288,000	$ 506,000	2,501,000	$ 1,063,000
Repayments of lines of credit				35,229,000	12,816,000
Borrowings, outstanding		31,900,000		31,900,000		27,500,000	$ 10,300,000
Term Loan
Debt Instrument [Line Items]
Credit facility maximum borrowing amount						$ 15,000,000
Interest expense		500,000		1,000,000
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
Warrants term						10 years
Fair value on issuance						$ 900,000
Debt discount						900,000
Deferred debt issuance costs		976,000		976,000		$ 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
Horizon Term Loan
Debt Instrument [Line Items]
Repayments of lines of credit						$ 4,900,000
Line of credit, prepayment penalty						$ 100,000
Maximum | Term Loan
Debt Instrument [Line Items]
Amortization of debt issuance costs				$ 300,000
Prior Term Loan
Debt Instrument [Line Items]
Interest expense			200,000		500,000
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	$ 25,000,000							$ 15,000,000
Unamortized debt issuance costs						$ 700,000
Mid Cap Credit Facility
Debt Instrument [Line Items]
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		20,400,000		$ 20,400,000		$ 16,500,000
Available balance of credit facility		1,100,000		1,100,000		1,400,000
Mid Cap Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	5.75%
Mid Cap Prior Term Loan
Debt Instrument [Line Items]
Term loan, borrowing								$ 7,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Interest expense		800,000	300,000	1,500,000	600,000
Amortization of debt issuance costs		$ 200,000	$ 100,000	$ 400,000	$ 200,000
Credit Facility and Term Loan
Debt Instrument [Line Items]
Line of credit facility covenant minimum liquidity requirement in unrestricted cash						$ 5,000,000