Fair Value Measurements - Summary of Changes in Fair Value for the Level 3 Liability (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (1,785)
Unrealized losses	(3,628)
Ending balance	(5,413)
Warrants
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(1,471)
Unrealized losses	(2,105)
Ending balance	(3,576)
Deferred Compensation
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(314)
Unrealized losses	(1,523)
Ending balance	$ (1,837)