Commitments and Contingencies - Additional Information (Detail)										1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 12, 2015 USD ($)	Sep. 28, 2015 USD ($)	May. 22, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jan. 13, 2015 USD ($) shares	Jan. 09, 2015 USD ($) shares	Mar. 07, 2011 USD ($)	Jan. 06, 2011	Aug. 24, 2004 Patent	Jul. 31, 2015 USD ($)	Mar. 31, 2016 USD ($) $ / shares shares	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012	Dec. 31, 2011 USD ($)	May. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Total rent Expense											$ 104,000	$ 177,000
Deferred rent - current portion											295,000		$ 348,000
Deferred rent-non-current portion											276,000		313,000
Deferred rent liability net											571,000		661,000
Research and Development Expense											10,199,000	74,249,000
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 million and no greater than $20 million per year.
Research and Development Service Agreement Aggregate Quarterly Payments											3,750,000
Offset costs in research and development expense											1,400,000
Deferred revenue - current portion											6,489,000		6,861,000
Deferred Revenue, long term											46,319,000		47,917,000
Research contract revenue											$ 1,969,000	272,000
Issuance of common stock in a license agreement												67,285,000
DEKK Tec Inc
Commitments and Contingencies Disclosure [Line Items]
Sale of stock price per share | $ / shares											$ 0.02
Outstanding options to purchase common stock | shares											13,808
Southern Research Institute
Commitments and Contingencies Disclosure [Line Items]
Royalty payment													25,000	$ 25,000	$ 25,000
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
Deferred revenue											0
Research contract revenue											$ 272,000
Estimated upfront payment for research and development funding earning period											75 months
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											0	$ 0
Predictive Therapeutics, Ltd.
Commitments and Contingencies Disclosure [Line Items]
Upfront payment received											250,000
Deferred revenue - current portion											100,000
Research contract revenue											100,000
Accounts receivable and cost reimbursement at default											311,000
Predictive Therapeutics, Ltd. | Development Regulatory And Sales Based Milestone
Commitments and Contingencies Disclosure [Line Items]
Upfront payment received	$ 250,000
Expected Additional milestone payments to be received											12,800,000
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
Payments for development and commercial milestones per Product											$ 413,000,000
Milestone payments, percentage											50.00%
Agreement commencement date											2015-05
Deferred revenue, revenue recognized											$ 1,600,000
Deferred revenue											52,700,000							$ 57,500,000
Deferred revenue - current portion											6,400,000
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
Prepaid Expenses and Other Current Assets
Commitments and Contingencies Disclosure [Line Items]
Pre paid research and development expenses											$ 13,600,000
Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Contract termination description											The Company's obligation to pay 50% 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
Intrexon Corporation | GVHDA Arrangement
Commitments and Contingencies Disclosure [Line Items]
Percent of company net profit											50.00%
Contract termination description											The Company's obligation to pay 50% 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 | Quarterly Payment
Commitments and Contingencies Disclosure [Line Items]
Percent of company net profit								50.00%
Percentage of revenue agreed to pay which is obtained from sublicensor								50.00%
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
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Operating lease expiration month and year			2016-08														2016-08
Loss on sublease															42,000
Remaining contractual obligation															367,000
Sublease revenue from subtenant			$ 105,000												325,000
Security deposits			$ 17,000								$ 128,000		$ 128,000
Sublease term amendment											Aug. 31, 2021
Security deposit from subtenant														$ 20,000
Boston, MA | The first floor
Commitments and Contingencies Disclosure [Line Items]
Loss on sublease				$ 167,000
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
Remaining contractual obligation															2,300,000
Sublease revenue from subtenant															1,600,000
Loss on disposal of fixed assets															$ (392,000)