Fair Value Measurements - Schedule of Reconciliation of Changes in the Fair Value of Financial Instruments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Change in fair value associated with convertible preferred stock tranche liability	$ 876
Reduction in tranche liability due to preferred stock issuance	(5,123)
Significant Unobservable Inputs (Level 3)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value as of January 1, 2017	4,247
Change in fair value associated with convertible preferred stock tranche liability	876
Reduction in tranche liability due to preferred stock issuance	$ (5,123)