Business - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended
	Oct. 05, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Nature Of Operations [Line Items]
Accumulated deficit		$ (761,209)		$ (712,442)
Cash and cash equivalents		31,728		$ 70,946	$ 84,406
Intrexon Corporation/Precigen
Nature Of Operations [Line Items]
Transaction advisory expenses		$ 300	$ 1,000
Subsequent Event | Gorilla IL-12 Products
Nature Of Operations [Line Items]
Percentage of development cost shared by other party	80.00%
Percentage of operating profit shared by other party	80.00%
Subsequent Event | Intrexon Corporation/Precigen
Nature Of Operations [Line Items]
Reimbursement of historical costs	$ 1,000
Additional milestone payment for exclusively licensed program to be paid	52,500
Maximum Royalty payable	$ 100,000
Percentage of sublicensing income	20.00%
Royalty payment to be received	$ 100,000
Transaction advisory costs	7,000
Subsequent Event | Intrexon Corporation/Precigen | License
Nature Of Operations [Line Items]
Annual Licensing fee	$ 100
Subsequent Event | Intrexon Corporation/Precigen | Gorilla IL-12 Products
Nature Of Operations [Line Items]
Percentage of development cost shared by other party	20.00%
Percentage of operating profit shared by other party	20.00%