Fair Value Measurement - Summary of Assumptions Used to Estimate Fair Value of Contingent Payments (Detail) - Level 3 [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Expected Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	114.9	95.3
Risk-free Interest Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	0.11	1.60
Cost of Capital [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	30	30
Measurement Input Probability Of Payment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	63
Projected Year of Payment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	2022
Minimum [Member] | Discount for Lack of Marketability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	9	8
Minimum [Member] | Measurement Input Probability Of Payment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments		31
Minimum [Member] | Projected Year of Payment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments		2020
Maximum [Member] | Discount for Lack of Marketability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	15	12
Maximum [Member] | Measurement Input Probability Of Payment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments		50
Maximum [Member] | Projected Year of Payment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments		2022
Weighted Average [Member] | Expected Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	114.9	95.3
Weighted Average [Member] | Risk-free Interest Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	0.11	1.60
Weighted Average [Member] | Cost of Capital [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	30	30
Weighted Average [Member] | Discount for Lack of Marketability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	12	10
Weighted Average [Member] | Measurement Input Probability Of Payment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	63	46
Weighted Average [Member] | Projected Year of Payment [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assumptions used to estimate fair value of contingent payments	2022	2020