Debt - MidCap Facility Agreement (Details) - USD ($)			12 Months Ended
	Mar. 31, 2018	Mar. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 01, 2016
Line of Credit Facility [Line Items]
Unamortized debt discount				$ 2,023,000	$ 3,543,000
Fifth amendment credit facility with MidCap | Revolving credit facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 22,500,000
Fifth amendment credit facility with MidCap | Term loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity						5,000,000
Debt instrument, prepayment fee						$ 600,000
Amended Credit Facility With Mid Cap
Line of Credit Facility [Line Items]
Maximum borrowing capacity				12,674,000	$ 17,873,000
Monthly term loan payments				200,000
Unamortized debt discount				$ 1,200,000
Amended Credit Facility With Mid Cap | Minimum
Line of Credit Facility [Line Items]
Effective date of financial covenants of Amended Credit Facility		2017-04
Amended Credit Facility With Mid Cap | Maximum
Line of Credit Facility [Line Items]
Effective date of financial covenants of Amended Credit Facility		2018-04
Amended Credit Facility With Mid Cap | Maximum | Line of credit
Line of Credit Facility [Line Items]
Debt default, interest rate increase				5.00%
Amended Credit Facility With Mid Cap | Forecast
Line of Credit Facility [Line Items]
Minimum liquidity covenant amount	$ 5,000,000
Latest effective date of minimum liquidity covenant	2019-03
Monthly term loan payments			$ 300,000
Amended Credit Facility With Mid Cap | Forecast | Minimum
Line of Credit Facility [Line Items]
Effective date of financial covenants of Amended Credit Facility	2018-04
Amended Credit Facility With Mid Cap | Forecast | Maximum
Line of Credit Facility [Line Items]
Effective date of financial covenants of Amended Credit Facility	2019-04
Amended Credit Facility With Mid Cap | Revolving credit facility
Line of Credit Facility [Line Items]
Line of credit				$ 10,300,000
Interest rate				7.36%
Amended Credit Facility With Mid Cap | Revolving credit facility | LIBOR
Line of Credit Facility [Line Items]
Interest rate description				LIBOR plus 6.0%
Basis spread				6.00%
Amended Credit Facility With Mid Cap | Term loan
Line of Credit Facility [Line Items]
Line of credit				$ 2,400,000
Floor on interest rate				9.50%
Interest rate				9.50%
Amended Credit Facility With Mid Cap | Term loan | LIBOR
Line of Credit Facility [Line Items]
Interest rate description				("LIBOR") plus 8.0%
Basis spread				8.00%