Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value hierarchy level 1 to level 2 transfers amount	$ 0		$ 0
Fair value hierarchy level 2 to level 1 transfers amount	0		0
Non-marketable equity securities					$ 400,000
Remeasurements or impairment losses on non-marketable equity securities	$ 0	$ 0	$ 0	$ 0