Summary of Significant Accounting Policies - Fair Value, Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities	$ 691	$ 86
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	408	479
Warrant liabilities	691	86
Total liabilities	691	86
Fair Value, Recurring | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit	408	479
Fair Value, Recurring | Letter of credit | Restricted cash, long term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit	408	408
Fair Value, Recurring | Letter of credit | Cash and restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit		71
Level I | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	408	479
Warrant liabilities	0	0
Total liabilities	0	0
Level I | Fair Value, Recurring | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit	408	479
Level II | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Warrant liabilities	0	0
Total liabilities	0	0
Level II | Fair Value, Recurring | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit	0	0
Level III | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Warrant liabilities	691	86
Total liabilities	691	86
Level III | Fair Value, Recurring | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letter of credit	$ 0	$ 0