Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended			12 Months Ended	0 Months Ended				12 Months Ended	0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 13, 2015	Jan. 09, 2015	Aug. 24, 2004 Patent	Dec. 31, 2004	Jan. 06, 2011	Mar. 07, 2011	Jun. 27, 2013	Aug. 30, 2013 sqft	Dec. 31, 2011	Oct. 17, 2013 sqft	Nov. 02, 2012	Oct. 15, 2014	Jun. 30, 2012 sqft	Jan. 31, 2012 sqft	Apr. 30, 2011 sqft
Commitments and Contingencies Disclosure [Line Items]
Loss on disposal of fixed assets										$ (585,000)	$ (48,000)
Total rent Expense									1,200,000	1,000,000	1,100,000
Deferred rent - current portion	280,000				212,000				280,000	212,000
Deferred rent-non-current portion	570,000				851,000				570,000	851,000
Deferred rent liability net	850,000				1,100,000				850,000	1,100,000
Research and Development Expense									32,706,000	42,852,000	83,446,000
Deferred revenue - current portion	1,360,000				800,000				1,360,000	800,000
Research contract revenue	340,000	633,000	200,000	200,000	200,000	200,000	200,000	200,000	1,373,000	800,000	800,000
Estimated upfront payment for research and development funding earning period										75 months
Subsequent Event
Commitments and Contingencies Disclosure [Line Items]
Research and development arrangement Terms												In connection with such transfer, the terms of the License also require us 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 Service Agreement Quarterly Payment												3,750,000
Period of milestone payment												60 days
Subsequent Event | License Agreement | Ziopharm
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement												10,124,561
Cash consideration for license agreement												50,000,000
Subsequent Event | License Agreement | Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement												50,000,000
Subsequent Event | Letter Agreement
Commitments and Contingencies Disclosure [Line Items]
Incentive shares issued period													60 days
Subsequent Event | Letter Agreement | Ziopharm
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement													1,597,602
Cash consideration for license agreement													7,500,000
Subsequent Event | Letter Agreement | Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Cash consideration for license agreement													7,500,000
Subsequent Event | Minimum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense												15,000,000
Subsequent Event | Maximum
Commitments and Contingencies Disclosure [Line Items]
Research and Development Expense												20,000,000
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									236,000
Intrexon Corporation
Commitments and Contingencies Disclosure [Line Items]
Contract termination description									Our obligation to pay 50% of net profits or revenue described above with respect to these "retained" products will survive termination of the Channel Agreement.
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%
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								13,808
Southern Research Institute
Commitments and Contingencies Disclosure [Line Items]
Milestone maximum payment	775,000								775,000
Royalty payment									25,000	25,000	25,000
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
PPD Development L. P.
Commitments and Contingencies Disclosure [Line Items]
Installment payments										9,200,000	3,800,000
Pharmaceutical Research Associates Inc | Upon the achievement of various milestones
Commitments and Contingencies Disclosure [Line Items]
Installment payments										2,200,000	7,300,000
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]
Other expense											200,000
Payment for consulting services fee									180,000	135,000
Harmon Hill LLC | Collaboration Agreement | Monthly Payment
Commitments and Contingencies Disclosure [Line Items]
Payment for consulting services fee																		15,000
Md Anderson Cancer Center | Subsequent Event | License Agreement
Commitments and Contingencies Disclosure [Line Items]
Contingent consideration of common stock payable period												60 days
Boston, MA
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease	21,184								21,184
Operating lease expiration month and year																				2016-08
Area under sublease agreement																			5,249
Loss on sublease										42,000
Remaining contractual obligation					367,000					367,000
Sublease revenue from subtenant										325,000
Loss on disposal of fixed assets										(194,000)
Security deposits	127,000				20,000				127,000	20,000	127,000
Security deposit from subtenant					20,000					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
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									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					2,300,000
Sublease revenue from subtenant										1,600,000
Loss on disposal of fixed assets										(392,000)
Germantown, MD
Commitments and Contingencies Disclosure [Line Items]
Office space under operating lease																										2,227
Operating lease expiration month and year																				2014-03
Security deposits																				4,000
Office closing date											Jul. 16, 2012