Fair Value Measurements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value assets transferred from level 1 to level 2	$ 0
Minimum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value inputs, probabilities of going public by term	6 months 18 days
Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value inputs, probabilities of going public by term	1 month 17 days
Probabilities of going public, percentage | Minimum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.125
Probabilities of going public, percentage | Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.80
Discount rate
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.30
Discount for lack of marketability | Minimum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.30
Discount for lack of marketability | Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.075
Expected term | Minimum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement term	2 years 9 months 18 days
Expected term | Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement term	3 years
Risk free interest rate | Minimum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.008
Risk free interest rate | Maximum
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.011
Expected volatility rate
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value input, Equity securities measurement	0.70