Commitments and Contingencies - Additional Information (Detail) $ in Thousands					1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 28, 2019 USD ($)	Oct. 05, 2018 USD ($)	Jan. 13, 2015 USD ($)	Aug. 24, 2004 USD ($) Patent	Jul. 31, 2015 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Nov. 28, 2020 USD ($)	Feb. 19, 2019 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Research and development expense						$ 8,641	$ 8,263	$ 28,115	$ 25,935
Research and development arrangement Terms											Pursuant to the Research and Development Agreement, the Company, Precigen and MD Anderson formed a joint steering committee to oversee and manage the new and ongoing research programs. Under the License Agreement with Precigen, the Company and Precigen agreed that Precigen would no longer participate on the joint steering committee after the date of the License Agreement. As provided under the MD Anderson License, the Company provided funding for research and development activities in support of the research programs under the Research and Development Agreement for a period of three years and in an amount of no less than $15.0 million and no greater than $20.0 million per year.
Cash balance						88,419		88,419		$ 61,729
Agreement commencement date											2015-05
Number of products | Patent				2
MD Anderson License and the Research and Development Agreement Member [Member]
Commitments and Contingencies Disclosure [Line Items]
Research and development service agreement aggregate quarterly payments								4,700	4,000
Cash resources on hand						21,500		21,500		27,800
CRADA Agreement [Member]
Commitments and Contingencies Disclosure [Line Items]
Obligations due under contract													$ 5,000
Remaining contractual obligation													$ 5,600
Quarterly payments under contract						600	600	1,900	1,900
Gorilla IL12 Products [Member] | Parent [Member]
Commitments and Contingencies Disclosure [Line Items]
Percentage of development costs		80.00%
Percentage of operating profits		80.00%
CAR Products [Member]
Commitments and Contingencies Disclosure [Line Items]
Royalty income						0		0
Amount of royalties receivable		$ 50,000
License Agreement with the National Cancer Institute [Member]
Commitments and Contingencies Disclosure [Line Items]
Expected cash payment payable per installments	$ 500
The University of Texas MD Anderson Cancer Center and The Texas A & M University System
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment				$ 4,500
ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Research and development expense							$ 36		$ 36
License Agreement with the National Cancer Institute [Member]
Commitments and Contingencies Disclosure [Line Items]
Reimbursement of historical costs	46
Expected Cash Payment Payable	1,500					1,000		1,000
Minimum Royalties Amount Payable	$ 300
Description Of First Annual Royalty Payable	The first minimum annual royalty payment is payable on the date that is eighteen months following the date of the Patent License
Description Of First Benchmark Payable	The first benchmark payment of $0.1 million will be due upon the initiation of the Company’s first sponsored phase 1 clinical trial of a licensed product or licensed process in the field of use licensed under the Patent License.
Description Of option To terminate Agreement	The NCI may terminate or modify the Patent License in the event of a material breach, including if the Company does not meet certain milestones by certain dates, or upon certain insolvency events that remain uncured following the date that is 90 days following written notice of such breach or insolvency event
Agreement termination, notice period	60 days
payments under the Patent License						500		500
License Agreement with the National Cancer Institute [Member] | Performance Based Payments Member [Member]
Commitments and Contingencies Disclosure [Line Items]
Aggregate Benchmark Payments Payable	$ 4,300
License Agreement with the National Cancer Institute [Member] | One Time Benchmark Payments [Member]
Commitments and Contingencies Disclosure [Line Items]
Potential Benchmark Payments Payable	12,000
License Agreement with the National Cancer Institute [Member] | Scenario, Forecast [Member]
Commitments and Contingencies Disclosure [Line Items]
Expected Cash Payment Payable												$ 1,500
Minimum Royalties Amount Payable												$ 100
License Agreement with the National Cancer Institute [Member] | Post Marketing Approval [Member] | Performance Based Payments Member [Member]
Commitments and Contingencies Disclosure [Line Items]
Aggregate Benchmark Payments Payable	3,000
License Agreement with the National Cancer Institute [Member] | licensed products [Member] | One Time Benchmark Payments [Member]
Commitments and Contingencies Disclosure [Line Items]
Maximum Sales Revenue On Which Benchmark Payments Payable	$ 1,000,000
Prepaid Expenses and Other Current Assets | MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Cash balance						18,400		18,400
Other Noncurrent Assets | MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Cash balance						9,400		9,400
Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Licensing fee					$ 115,000
Research and development expense										$ 1,000
Milestone payment receivable						$ 5,000		$ 5,000
Milestone payment receivable period								2 years
Upfront payment received					$ 57,500
Percentage of upfront fee Payable					50.00%
Annual Licensing fee		100
Reimbursement of historical costs		1,000
Expected additional milestones payable		$ 52,500
Intrexon Corporation | Gorilla IL12 Products [Member]
Commitments and Contingencies Disclosure [Line Items]
Percentage of development costs		20.00%
Percentage of operating profits		20.00%
Intrexon Corporation | T-cell receptor
Commitments and Contingencies Disclosure [Line Items]
Maximum royalty amount		$ 100,000
Portion of income payable to related party		20.00%
Minimum | MD Anderson License and the Research and Development Agreement Member [Member]
Commitments and Contingencies Disclosure [Line Items]
Research and development expense			$ 15,000
Maximum | MD Anderson License and the Research and Development Agreement Member [Member]
Commitments and Contingencies Disclosure [Line Items]
Research and development expense			$ 20,000