Fair Value Measurements - Reconciliation of Common Stock Warrant Liability Measured at Fair Value on Recurring Basis (Details) - Recurring basis - Significant Unobservable Inputs (Level 3) - Total $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of derivative liabilities at December 31, 2017	$ 76
Change in the fair value of derivative liabilities, net	(27)
Adjustment for conversions of Notes	0
Fair value of derivative liabilities at March 31, 2018	49
Common stock warrant liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of derivative liabilities at December 31, 2017	76
Change in the fair value of derivative liabilities, net	(27)
Adjustment for conversions of Notes	0
Fair value of derivative liabilities at March 31, 2018	49
Embedded derivative liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of derivative liabilities at December 31, 2017	0
Change in the fair value of derivative liabilities, net	0
Adjustment for conversions of Notes	0
Fair value of derivative liabilities at March 31, 2018	$ 0