Commitments and Contingencies - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended	12 Months Ended			0 Months Ended							12 Months Ended
	Jan. 13, 2015	Mar. 31, 2015	Mar. 31, 2014	Apr. 13, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 24, 2004 Patent	Mar. 07, 2011	Jun. 27, 2013	Jan. 06, 2011	Jan. 09, 2015	Oct. 17, 2013 sqft	Aug. 30, 2013 sqft	Dec. 31, 2011	Oct. 15, 2014	Jun. 30, 2014	Nov. 02, 2012	Jan. 31, 2012 sqft	Jun. 30, 2012 sqft
Commitments and Contingencies Disclosure [Line Items]
Total rent Expense		$ 177,000	$ 167,000
Deferred rent - current portion		405,000	224,000		280,000
Deferred rent-non-current portion		553,000	792,000		570,000
Deferred rent liability net		958,000	1,000,000
Research and development arrangement Terms	In connection with such transfer, the terms of the License also require the Company and Intrexon to enter into a research and development agreement with MD Anderson pursuant to which the Company will provide funding for certain research and development activities of MD Anderson for a period of three years
Research and Development Expense		74,249,000	6,542,000
Research contract revenue		272,000	200,000
Deferred revenue - current portion		1,088,000			1,360,000
Estimated upfront payment for research and development funding earning period			75 months
Subsequent Event
Commitments and Contingencies Disclosure [Line Items]
Research and Development Service Agreement Quarterly Payment				3,750,000
DEKK Tec Inc
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment																4,000,000
Option to purchase common stock		27,616
Sale of stock price per share		$ 0.02
Outstanding options to purchase common stock		13,808
Southern Research Institute
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment					775,000
Royalty payment					25,000	25,000	25,000
The University of Texas M.D. Anderson Cancer Center and The Texas A & M University System
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment																	4,500,000
Option to purchase common stock		50,222
Sale of stock price per share		$ 0.002
Number of products								2
The University of Texas M.D. 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 expected to vest																	12,556
Novella Clinical, Inc.
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment																		790,000
Number of amendments signed		2
Novella Clinical, Inc. | Upon the achievement of various milestones
Commitments and Contingencies Disclosure [Line Items]
Installment payments							256,000
Novella Clinical, Inc. | Upon two database related milestones
Commitments and Contingencies Disclosure [Line Items]
Installment payments						136,000
Novella Clinical, Inc. | Upon three clinical milestones
Commitments and Contingencies Disclosure [Line Items]
Installment payments		10,000			236,000
Baxter Healthcare Corporation | Upon the successful U.S. IND application for indibulin
Commitments and Contingencies Disclosure [Line Items]
Installment payments					250,000	250,000	250,000
Solasia
Commitments and Contingencies Disclosure [Line Items]
Upfront payment received									5,000,000
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
Harmon Hill LLC | Collaboration Agreement
Commitments and Contingencies Disclosure [Line Items]
Payment for consulting services fee		45,000	45,000
Monthly Payment | Harmon Hill LLC | Collaboration Agreement
Commitments and Contingencies Disclosure [Line Items]
Payment for consulting services fee										15,000
Per Product
Commitments and Contingencies Disclosure [Line Items]
Payments for development and commercial milestones per Product		413,000,000
First Two Products
Commitments and Contingencies Disclosure [Line Items]
Payments for development and commercial milestones per Product		826,000,000
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
License Agreement
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense		67,285,000
Issuance of common stock in licensing agreement, shares		11,722,163
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.
Percentage of up licensing fee paid		50.00%
Percentage of royalty paid		50.00%
Milestone payments, percentage		50.00%
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%
Intrexon Corporation | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement												7,500,000
Intrexon Corporation | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement	50,000,000
Ziopharm | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Common stock issued for cash												1,597,602
Cash consideration for license agreement												7,500,000
Ziopharm | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Common stock issued for cash	10,124,561
Cash consideration for license agreement	50,000,000
ARES Trading S.A.
Commitments and Contingencies Disclosure [Line Items]
Licensing fee		115,000,000
New York, NY
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease							7,259								6,251
Letter of credit		388,000					388,000								388,000
Additional office space under operating lease																			1,008
Operating lease expiration month and year						2018-10	2018-10
Area under sublease agreement													7,259
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)
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease		21,184
Operating lease expiration month and year															2016-08
Area under sublease agreement														5,249
Loss on sublease		167,000
Security deposits		127,000
Security deposit from subtenant					20,000
Boston, MA | The first floor
Commitments and Contingencies Disclosure [Line Items]
Operating lease space															5,249
Boston, MA | The second floor
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease																				4,113
Operating lease space															8,538
Boston, MA | The third floor
Commitments and Contingencies Disclosure [Line Items]
Operating lease space															6,959
Boston, MA | The four floor
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease																				9,800
Security deposits																				41,000