Fair Value Measurements - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset measured and recognized at fair value on recurring basis	$ 0	$ 0
Share settled liabilities		0
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liability measured and recognized at fair value on non-recurring basis	300,000
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalent at recurring basis	0	0
Fair Value Measurements, Non-recurring | Fair Value, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Privately-held investments measured at fair value	$ 300,000	$ 300,000