Commitments and Contingencies - Additional Information (Detail)		3 Months Ended		9 Months Ended		36 Months Ended	78 Months Ended
	Nov. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)	Jan. 31, 2018 USD ($) ft²	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Rent expense per month				$ 120,000
Base rent escalators		3.00%		3.00%		3.00%	3.00%
Office space under lease agreement | ft²				45,580
Landlord tenant improvements funded amount	$ 500,000
Area of leased office space | ft²						5,803
Lease term						36 months
Lease rental period start date						Feb. 01, 2015
Lease rental period end date						Jan. 31, 2018
Base rent under the lease						$ 12,000
Leasehold improvements							$ 518,000
Rent expense		$ 264,000	$ 362,000	$ 915,000	$ 1,094,000
Lease Term For Remainder of Total Rentable Square Footage [Member]
Commitments And Contingencies [Line Items]
Lease expiration date				Sep. 01, 2024
Lease option termination description				option to terminate the lease on or after September 1, 2019 with 9 months prior written notice.
Lease For 14,685 of Total Rentable Square Footage [Member]
Commitments And Contingencies [Line Items]
Office space under lease agreement | ft²				14,685
Lease expiration date				Oct. 31, 2018
Lease Amendment
Commitments And Contingencies [Line Items]
Lease expiration date				Aug. 31, 2024
Lease Amendment | Maximum [Member]
Commitments And Contingencies [Line Items]
Tenant improvements		$ 500,000		$ 500,000			$ 500,000