Commitments and Contingencies - Additional Information (Detail)			3 Months Ended		9 Months Ended		66 Months Ended
	Dec. 28, 2015 USD ($) ft²	Jan. 09, 2015 USD ($) ft²	Dec. 31, 2017 USD ($) Lease	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) ft² Lease	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Lease
Commitments And Contingencies [Line Items]
Number of non-cancelable leases | Lease			2		2		2
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
Area of leased office space | ft²	12,088	5,803
Lease term		36 months
Lease rental period start date	Feb. 01, 2016	Feb. 01, 2015
Lease rental period end date	Jan. 31, 2017	Jan. 31, 2018
Base rent under the lease	$ 15,000	$ 12,000
Leasehold improvements							$ 518,000
Rent expense			$ 362,000	$ 307,000	$ 1,094,000	$ 912,000
Lease Term For Remainder of Rentable Square Footage [Member]
Commitments And Contingencies [Line Items]
Lease expiration date					Sep. 01, 2021
Lease option termination description					option to terminate this lease on or after September 1, 2019
Lease Term 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					Dec. 15, 2018