Commitments and Contingencies - Additional Information (Detail)								1 Months Ended				3 Months Ended		12 Months Ended				32 Months Ended
	Jun. 29, 2016 $ / shares shares	Sep. 28, 2015 USD ($)	Jan. 13, 2015 USD ($) shares	Jan. 09, 2015 USD ($) shares	Mar. 07, 2011 USD ($)	Jan. 06, 2011	Aug. 24, 2004 Patent	Nov. 30, 2017 USD ($)	May 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012	Dec. 31, 2011 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Jan. 30, 2018 USD ($) ft²	Dec. 31, 2014 USD ($) shares
Commitments and Contingencies Disclosure [Line Items]
Loss on sublease												$ 176,000	$ 172,000					$ 40,000
Deferred rent - current portion												102,000						141,000
Deferred rent-non-current portion												3,000						1,000
Deferred rent liability net												105,000						142,000
Research and Development Expense												10,183,000	11,967,000
Cash balance												$ 51,108,000	66,447,000					$ 70,946,000
Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Preferred stock, stated value | $ / shares												$ 1,200						$ 1,200
Intrexon Corporation/Precigen | Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in licensing agreement, shares | shares	100,000											3,624
Preferred stock, stated value | $ / shares	$ 1,200
ECP Channel Agreement | Intrexon Corporation/Precigen
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit												20.00%
Percentage of revenue agreed to pay which is obtained from sublicensor												50.00%
Contract termination description												With respect to these "retained" Ziopharm Products, the Company's obligation to pay 20% of net profits derived from the sale of Ziopharm Products and 50% of revenue derived from a sublicensor will survive termination of the Channel Agreement.
ECP Channel Agreement | Intrexon Corporation/Precigen | Quarterly Payment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit						20.00%
Percentage of revenue agreed to pay which is obtained from sublicensor						50.00%
ECP Channel Agreement | Intrexon Corporation/Precigen | Quarterly Payment | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit	20.00%
ECP Channel Agreement | Intrexon Corporation/Precigen | Quarterly Payment | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit	50.00%
2016 GvHD Amendment | Intrexon Corporation/Precigen
Commitments and Contingencies Disclosure [Line Items]
Licensing fee		$ 10,000,000
Research and Development Expense										$ 10,000,000
2016 GvHD Amendment | Intrexon Corporation/Precigen | Quarterly Payment | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit	20.00%
2016 GvHD Amendment | Intrexon Corporation/Precigen | Quarterly Payment | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit	50.00%
License Agreement | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in licensing agreement, shares | shares												11,722,163		11,722,163
Research and Development Expense												$ 67,300,000		$ 67,300,000
Common stock issued for cash | shares			10,124,561
Cash consideration for license agreement			$ 50,000,000
License Agreement | The University of Texas MD Anderson Cancer Center and The Texas A & M University System
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment																				$ 4,500,000
Number of products | Patent							2
Options to purchase common stock | shares												50,222
Shares vested | shares																				37,666
License Agreement | The University of Texas MD Anderson Cancer Center and The Texas A & M University System | Research and Development Expense
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in a license agreement												$ 87,000
License Agreement | The University of Texas MD Anderson Cancer Center and The Texas A & M University System | Upon enrollment of the first patient in a multi-center pivotal clinical trial
Commitments and Contingencies Disclosure [Line Items]
Shares vested | shares																				12,556
License Agreement | Baxter Healthcare Corporation | Upon the successful U.S. IND application for indibulin
Commitments and Contingencies Disclosure [Line Items]
Installment payments								$ 250,000				0	0
License Agreement | Intrexon Corporation/Precigen | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement			50,000,000
Letter Agreement | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Common stock issued for cash | shares				1,597,602
Cash consideration for license agreement				$ 7,500,000
Letter Agreement | Intrexon Corporation/Precigen | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement				$ 7,500,000
ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense												$ 36,000
Agreement commencement date												2015-05
Agreement termination, notice period												90 days
ARES Trading License | Development Milestone Payments
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per product												$ 60,000,000
ARES Trading License | Regulatory Milestone Payments
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per product												148,000,000
ARES Trading License | Commercial Milestone Payments
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per product												205,000,000
ARES Trading License | Intrexon Corporation/Precigen
Commitments and Contingencies Disclosure [Line Items]
Licensing fee											$ 115,000,000
Milestone payment receivable												$ 5,000,000
Milestone payment receivable period												2 years
Upfront payment received											$ 57,500,000
Percentage of upfront fee payable											50.00%
Milestone maximum payment												$ 50,000,000
Milestone payments, percentage												50.00%
ARES Trading License | Intrexon Corporation/Precigen | Substantive Milestones
Commitments and Contingencies Disclosure [Line Items]
Potential milestone payment												$ 15,000,000
Collaboration Agreement | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Installment payments									$ 1,000,000
Collaboration Agreement | Solasia
Commitments and Contingencies Disclosure [Line Items]
Upfront payment received					$ 5,000,000
Milestone payment received									$ 1,000,000
Collaboration Agreement | Solasia | Development-based milestones
Commitments and Contingencies Disclosure [Line Items]
Expected additional milestone payments to be received												32,500,000
Collaboration Agreement | Solasia | Sales-based milestones
Commitments and Contingencies Disclosure [Line Items]
Expected additional milestone payments to be received												$ 53,500,000
Cooperative Research and Development Agreement
Commitments and Contingencies Disclosure [Line Items]
Research and development arrangement Terms												Pursuant to the Research and Development Agreement, the Company, Intrexon and MD Anderson have agreed to form a joint steering committee that will oversee and manage the new and ongoing research programs. As provided under the MD Anderson License, the Company will provide 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.
Cooperative Research and Development Agreement | Minimum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense			15,000,000
Cooperative Research and Development Agreement | Maximum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense			$ 20,000,000
Cooperative Research and Development Agreement | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Research and Development Service Agreement Payment												$ 2,700,000	3,800,000
Cooperative Research and Development Agreement | M.D. Anderson Cancer Center
Commitments and Contingencies Disclosure [Line Items]
Funding used to offset costs in research and development expense												9,500,000
Cash balance												32,400,000
Cooperative Research and Development Agreement | M.D. Anderson Cancer Center | Prepaid Expenses and Other Current Assets
Commitments and Contingencies Disclosure [Line Items]
Cash balance												18,500,000
Cooperative Research and Development Agreement | M.D. Anderson Cancer Center | Other Noncurrent Assets
Commitments and Contingencies Disclosure [Line Items]
Cash balance												13,900,000
Cooperative Research and Development Agreement | Intrexon Corporation/Precigen | National Cancer Institute
Commitments and Contingencies Disclosure [Line Items]
Obligation for payment												4,400,000
Miles stone payment payable												625,000
Milestone payment paid												625,000
New York, NY
Commitments and Contingencies Disclosure [Line Items]
Letter of credit												388,000					$ 388,000
Operating lease expiration month and year																2018-10
Loss on sublease															$ 729,000
Obligation for payment															2,300,000
Sublease revenue from subtenant															$ 1,600,000
Loss on sublease												31,000	$ 31,000
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Operating lease expiration month and year																	2016-08
Security deposits												$ 128,000
Sublease term amendment												Aug. 31, 2021
Houston, TX
Commitments and Contingencies Disclosure [Line Items]
Operating lease area | ft²																			210
Operating leases future minimum monthly payment due through year 2021																			$ 1,000