Commitments and Contingencies - Additional Information (Detail)									1 Months Ended			3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) $ / shares	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 ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Mar. 31, 2017 USD ($) $ / shares shares	Mar. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012	Dec. 31, 2011 USD ($)	Jan. 10, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares	May 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares
Commitments and Contingencies Disclosure [Line Items]
Total rent Expense												$ 172,000	$ 104,000
Deferred rent - current portion	$ 162,000											162,000								$ 155,000
Deferred rent-non-current portion	89,000											89,000								126,000
Deferred rent liability net	251,000											251,000								281,000
Research and Development Expense												$ 11,967,000	10,199,000
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												$ 3,800,000		$ 3,800,000
Offset costs in research and development expense												4,600,000
Deferred revenue - current portion	6,389,000											6,389,000								6,389,000
Deferred Revenue, long term	39,931,000											$ 39,931,000								41,528,000
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	1,000,000
Miles stone payment payable													1,000,000	$ 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]
Milestone payment receivable												0	272,000
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												0	0
Baxter Healthcare Corporation | Upon the successful U.S. IND application for indibulin | Scenario, Forecast
Commitments and Contingencies Disclosure [Line Items]
Additional payment payable amount									$ 250,000
License Agreement
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense												$ 67,300,000			$ 67,300,000
Issuance of common stock in licensing agreement, shares | shares												11,722,163			11,722,163
ARES Trading License
Commitments and Contingencies Disclosure [Line Items]
Agreement termination, notice period												90 days
Milestone payments, percentage												50.00%
Agreement commencement date												2015-05
Deferred revenue, revenue recognized												$ 1,600,000	$ 1,600,000
Deferred revenue, upfront payment	$ 46,300,000											$ 46,300,000								$ 47,900,000	$ 57,500,000
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
Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Preferred stock, stated value | $ / shares	$ 1,200											$ 1,200								$ 1,200
Prepaid Expenses and Other Current Assets
Commitments and Contingencies Disclosure [Line Items]
Pre paid research and development expenses	$ 25,400,000											$ 25,400,000
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
Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Contract termination description												The Company's obligation to pay 20% of net profits or revenue described above with respect to these "retained" products 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
Intrexon Corporation | 2016 GvHD Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit												20.00%
Contract termination description												The Company's obligation to pay 20% of net profits or revenue with respect to these "retained" products will survive termination of the GvHD Agreement.
Licensing fee			$ 10,000,000
Research and Development Expense										$ 10,000,000
Agreement termination period			24 months
Agreement termination, notice period			90 days
Intrexon Corporation | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement				$ 50,000,000
Intrexon Corporation | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement					$ 7,500,000
Intrexon Corporation | Cooperative Research and Development Agreement | National Cancer Institute
Commitments and Contingencies Disclosure [Line Items]
Obligation for payment																			$ 7,500,000
Miles stone payment payable																			$ 625,000
Milestone payment paid												$ 625,000
Intrexon Corporation | 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 | Quarterly Payment | 2016 GvHD Amendment | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit		20.00%
Intrexon Corporation | Quarterly Payment | 2016 GvHD Amendment | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit		50.00%
Intrexon Corporation | Quarterly Payment | ECP Channel Agreement | After Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit		20.00%
Intrexon Corporation | Quarterly Payment | ECP Channel Agreement | Before Amendment
Commitments and Contingencies Disclosure [Line Items]
Royalty percentage of net profit		50.00%
Intrexon Corporation | Series 1 Preferred Stock
Commitments and Contingencies Disclosure [Line Items]
Issuance of common stock in licensing agreement, shares | shares		100,000										3,216
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
New York, NY
Commitments and Contingencies Disclosure [Line Items]
Letter of credit	388,000											$ 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
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Operating lease expiration month and year																		2016-08
Security deposits	$ 128,000											$ 128,000			$ 128,000
Sublease term amendment	Aug. 31, 2021