Fair Value Measurements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value assets transferred from level 1 to level 2	$ 0
Fair value inputs, discount rate	30.00%
Fair value assumptions, expected volatility rate	70.00%
Minimum [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value inputs, probabilities of going public, percentage	12.50%
Fair value inputs, probabilities of going public by term	6 months 18 days
Fair value inputs, discount for lack of marketability	30.00%
Fair value assumptions, expected term	2 years 9 months 18 days
Fair value assumptions, risk free interest rate	0.80%
Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value inputs, probabilities of going public, percentage	80.00%
Fair value inputs, probabilities of going public by term	1 month 17 days
Fair value inputs, discount for lack of marketability	7.50%
Fair value assumptions, expected term	3 years
Fair value assumptions, risk free interest rate	1.10%