Investments in Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Mar. 10, 2017	Nov. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) shares	Jun. 30, 2016 $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Noncash dividend income on preferred shares					$ 16,756	$ 7,421	$ 0
Purchase of preferred stock					1,161	2,308	17,080
Fair value of financial assets measured at fair value on a recurring basis					183,173	335,307
Receivables converted to preferred stock					$ 3,385	$ 0	$ 0
Fibrocell Science, Inc.
Schedule of Investments [Line Items]
Convertible preferred shares, shares issued | shares			1,161
Number of common shares into which warrants are convertible (in shares) | shares			498,843
Stockholders' equity reverse stock split conversion ratio	0.3333
Preferred stock, dividend rate, percentage					4.00%
Stockholders' equity, reverse stock split	1-for-3
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Preferred shares, stated value (in usd per share) | $ / shares				$ 1,200
Threshold consecutive trading days, conversion in shares					20 days
Preferred shares, dividend rate (in usd per share) | $ / shares					$ 12.00
Preferred shares, dividend rate, for unconverted shares after conversion event (in usd per share) | $ / shares					24.00
Minimum | ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Preferred shares, conversion calculation, divisor (in usd per share) | $ / shares					$ 1.00
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Dividend income, number of preferred shares received (in shares) | shares					13,460	6,184
Other Contractual Payments | Upfront and Milestone Payments | ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Collaborative arrangement consideration received, number of preferred shares (in shares) | shares				100,000
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Noncash dividend income on preferred shares					$ 16,717	$ 7,421
Fibrocell Science, Inc.
Schedule of Investments [Line Items]
Purchase of preferred stock			$ 1,161
Preferred stock
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis					161,225	129,545
Preferred stock | ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis					160,832	$ 129,545
Preferred stock | Oragenics, Inc.
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis					$ 0
Receivables converted to preferred stock		$ 3,385
Preferred stock, initial dividend rate					12.00%
Preferred stock, subsequent dividend rate					20.00%
Preferred stock | Fibrocell Science, Inc.
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis					$ 393