Commitments and Contingencies - Additional Information (Detail)										1 Months Ended		3 Months Ended		12 Months Ended						32 Months Ended
	Jan. 13, 2018 USD ($)	Jan. 01, 2018 USD ($)	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	Sep. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares	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 ($) ft²	Mar. 31, 2016 USD ($)	May 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares
Commitments and Contingencies Disclosure [Line Items]
Total rent expense														$ 700,000	$ 300,000	$ 1,000,000				$ 40,000
Deferred rent - current portion												$ 141,000	$ 155,000	141,000	155,000					141,000
Deferred rent-non-current portion												1,000	126,000	1,000	126,000					1,000
Deferred rent liability net												145,000	281,000	145,000	281,000					145,000
Research and Development Expense														$ 45,084,000	157,791,000	106,785,000
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.
Research and Development Service Agreement Aggregate Quarterly Payments														$ 13,000,000	15,000,000
Offset costs in research and development expense														7,300,000
Cash balance												70,946,000	81,053,000	70,946,000	81,053,000	140,717,000				70,946,000				$ 42,803,000
Research and Development Service Agreement Final Payments														39,200,000
Deferred revenue - current portion												6,389,000	6,389,000	6,389,000	6,389,000					6,389,000
Deferred Revenue, long term												35,139,000	41,528,000	$ 35,139,000	41,528,000					35,139,000
Issuance of common stock in a license agreement																$ 67,285,000
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
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
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
Solasia
Commitments and Contingencies Disclosure [Line Items]
Upfront payment received							$ 5,000,000
Milestone payment received																						$ 1,000,000
Milestone Payments Payable																						$ 1,000,000
Solasia | Development-based milestones
Commitments and Contingencies Disclosure [Line Items]
Expected Additional milestone payments to be received														32,500,000
Solasia | Sales-based milestones
Commitments and Contingencies Disclosure [Line Items]
Expected Additional milestone payments to be received														53,500,000
Baxter Healthcare Corporation | Upon the successful U.S. IND application for indibulin
Commitments and Contingencies Disclosure [Line Items]
Installment payments														$ 250,000
License Agreement
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in licensing agreement, shares | shares					11,722,163									11,722,163		11,722,163
Research and Development Expense														$ 67,300,000		$ 67,300,000
ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense														$ 1,600,000
Milestone payments, percentage														50.00%
Agreement commencement date														2015-05
Agreement termination, notice period														90 days
Deferred revenue, revenue recognized												1,600,000	1,600,000	$ 1,600,000	1,600,000
Deferred revenue, upfront payment												41,500,000	$ 47,900,000	41,500,000	$ 47,900,000					41,500,000			$ 57,500,000
MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Cash balance												$ 31,900,000		$ 31,900,000						$ 31,900,000
Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Preferred stock, stated value | $ / shares												$ 1,200	$ 1,200	$ 1,200	$ 1,200					$ 1,200
Development Milestone Payments | ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per Product														$ 60,000,000
Regulatory Milestone Payments | ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per Product														148,000,000
Commercial Milestone Payments | ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Payments for development, regulatory and commercial milestones per Product														205,000,000
Substantive Milestones
Commitments and Contingencies Disclosure [Line Items]
Potential milestone payment												$ 15,000,000		15,000,000						$ 15,000,000
Subsequent Event
Commitments and Contingencies Disclosure [Line Items]
Research and Development Service Agreement Final Payments	$ 34,600,000
Subsequent Event | MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Research and Development Service Agreement Final Payments		$ 2,700,000
Prepaid Expenses and Other Current Assets | MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Cash balance												18,500,000		18,500,000						18,500,000
Other Noncurrent Assets | MD Anderson License
Commitments and Contingencies Disclosure [Line Items]
Cash balance												13,400,000		$ 13,400,000						13,400,000
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.
Licensing fee				$ 10,000,000							$ 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		$ 50,000,000						50,000,000
Intrexon Corporation/Precigen | 2016 GvHD Amendment
Commitments and Contingencies Disclosure [Line Items]
Licensing fee				$ 10,000,000
Research and Development Expense										$ 10,000,000
Intrexon Corporation/Precigen | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement					$ 50,000,000
Intrexon Corporation/Precigen | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement						$ 7,500,000
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%
Intrexon Corporation/Precigen | Quarterly Payment | 2016 GvHD Amendment | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit			20.00%
Intrexon Corporation/Precigen | Quarterly Payment | 2016 GvHD Amendment | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit			50.00%
Intrexon Corporation/Precigen | Quarterly Payment | ECP Channel Agreement | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit			20.00%
Intrexon Corporation/Precigen | Quarterly Payment | ECP Channel Agreement | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit			50.00%
Intrexon Corporation/Precigen | Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in licensing agreement, shares | shares			100,000											13,460
Preferred stock, stated value | $ / shares			$ 1,200
ZIOPHARM | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Common stock issued for cash | shares					10,124,561
Cash consideration for license agreement					$ 50,000,000
ZIOPHARM | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Common stock issued for cash | shares						1,597,602
Cash consideration for license agreement						$ 7,500,000
Minimum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense					15,000,000
Maximum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense					$ 20,000,000
New York, NY
Commitments and Contingencies Disclosure [Line Items]
Letter of credit												388,000		$ 388,000					$ 388,000	388,000
Operating lease expiration month and year																		2018-10
Loss on sublease																	$ 729,000
Remaining contractual obligation																	2,300,000
Sublease revenue from subtenant																	$ 1,600,000
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Operating lease expiration month and year																			2016-08
Security deposits												$ 128,000	$ 128,000	$ 128,000	$ 128,000					$ 128,000
Sublease term amendment														Aug. 31, 2021
Houston, TX | Subsequent Event
Commitments and Contingencies Disclosure [Line Items]
Operating lease area | ft²																					210
Operating Leases Future Minimum Monthly Payment Due Through Year 2021																					$ 1,000