Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014 Entity	Jun. 30, 2013	Jun. 30, 2014 Segment Entity	Jun. 30, 2013	Dec. 31, 2013 Entity
Organization And Significant Accounting Policies [Line Items]
Research and development commitments with third parties			$ 2,647		$ 2,445
Research and development commitments with third parties not incurred	1,049		1,049		957
Maturity period of liquid investment			3 months
Cash equivalent investments in highly liquid money market accounts	67,792		67,792		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	309,486		309,486		330,086
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	(33,777)	7,734	(11,855)	(21,635)
Percentage of recognized income tax positions			50.00%
Number of segment			1
Property and equipment	17,389		17,389		16,629
HUNGARY
Organization And Significant Accounting Policies [Line Items]
Property and equipment	1,390		1,390
Equity Securities
Organization And Significant Accounting Policies [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	134,895		134,895		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	15,758		15,758		22,161
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	(7,113)	(865)	(6,403)	2,028
Ziopharm Oncology, Inc.
Organization And Significant Accounting Policies [Line Items]
Company's ownership percentage	16.30%		16.30%		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	66,053		66,053		71,134
Unrealized appreciation (depreciation) in the fair value of the Company's equity securities	$ (9,015)	$ 3,789	$ (5,081)	$ (27,743)
Minimum | Patents and Related Technologies
Organization And Significant Accounting Policies [Line Items]
Expected useful life of intangible asset			7 years
Minimum | Leasehold Improvements
Organization And Significant Accounting Policies [Line Items]
Property plant and equipment, useful life			1 year
Maximum | Patents and Related Technologies
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			4 years