Fair Value Measurements - Schedule of Reconciliations of Changes in the Fair Value of Financial Instruments (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Change in fair value associated with convertible preferred stock tranche liability	$ 876,000
Significant Unobservable Inputs (Level 3)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value as of January 1, 2017	$ 4,247,000	$ 4,247,000
Change in fair value associated with convertible preferred stock tranche liability		876,000
Reduction in tranche liability due to preferred stock issuance		$ (5,123,000)