Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014 Entity	Sep. 30, 2013	Sep. 30, 2014 Segment Entity	Sep. 30, 2013	Dec. 31, 2013 Entity
Organization And Significant Accounting Policies [Line Items]
Research and development commitments with third parties	$ 3,201		$ 3,201		$ 2,445
Research and development commitments with third parties not incurred	1,451		1,451		957
Maturity period of liquid investment			3 months
Cash equivalent investments in highly liquid money market accounts	18,717		18,717		43,733
Number of collaborators over which the Company has significant influence	2		2		2
Fair value of financial assets measured at fair value on a recurring basis	247,574		247,574		330,086
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	(37,089)	27,339	(48,944)	5,704
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Percentage of recognized income tax positions			50.00%
Number of segment			1
Property and equipment	35,596		35,596		16,629
HUNGARY
Organization And Significant Accounting Policies [Line Items]
Property and equipment	1,251		1,251
Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	97,806		97,806		141,525
Oragenics, Inc.
Organization And Significant Accounting Policies [Line Items]
Company's ownership percentage	24.40%		24.40%		24.60%
Oragenics, Inc. | Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	10,271		10,271		22,161
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	(5,487)	(1,262)	(11,890)	766
Ziopharm Oncology, Inc.
Organization And Significant Accounting Policies [Line Items]
Company's ownership percentage	16.00%		16.00%		16.40%
Ziopharm Oncology, Inc. | Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	43,270		43,270		71,134
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	$ (22,783)	$ 24,766	$ (27,864)	$ (2,977)
Minimum
Organization And Significant Accounting Policies [Line Items]
Expected useful life of intangible asset			3 years
Minimum | Leasehold Improvements
Organization And Significant Accounting Policies [Line Items]
Property plant and equipment, useful life			1 year
Maximum
Organization And Significant Accounting Policies [Line Items]
Expected useful life of intangible asset			14 years
Maximum | Leasehold Improvements
Organization And Significant Accounting Policies [Line Items]
Property plant and equipment, useful life			20 years