Fair Value Measurements - Summary of Changes in Fair Value for the Level 3 Liability (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (1,785)
Unrealized losses	(3,987)
Ending balance	(5,772)
Warrants
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(1,471)
Unrealized losses	(2,615)
Ending balance	(4,086)
Deferred Compensation
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(314)
Unrealized losses	(1,372)
Ending balance	$ (1,686)