Commitments and Contingencies - Rent Expense (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Initial recognition as of January 1, 2019			$ 1,168,000
Right-of-use Asset Amortization Expense			(123,000)
Balance as of September 30, 2019	$ 1,045,000		1,045,000
Rent expense	$ 65,000		$ 196,000
Rent expense, before ASU 2016-02		$ 65,000		$ 195,000