Investments in Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 10, 2017	Mar. 31, 2017 USD ($) shares	Jun. 30, 2016 $ / shares shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($) shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) shares	Dec. 31, 2016 USD ($)
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis				$ 226,215		$ 226,215		$ 335,307
Noncash Dividend Income						12,303	$ 3,676
Purchases of preferred stock and warrants						1,161	$ 2,308
Preferred stock
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis				$ 148,499		$ 148,499		129,545
Fibrocell Science, Inc.
Schedule of Investments [Line Items]
Convertible preferred shares issued (in shares) | shares		1,161
Number of common shares into which warrants are convertible (in shares) | shares		498,843
Reverse stock split ratio	1-for-3
Reverse stock split, conversion ratio	0.3333
Convertible preferred shares, dividend rate						4.00%
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Preferred shares, stated value (in usd per share) | $ / shares			$ 1,200
Threshold consecutive trading days, conversion of 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
ZIOPHARM Oncology, Inc. | Minimum
Schedule of Investments [Line Items]
Preferred shares, conversion calculation, divisor (in usd per share) | $ / shares						$ 1.00
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]
Dividend income, number of preferred shares received (in shares) | shares				3,414	3,063	9,943	3,063
Noncash Dividend Income				$ 4,311	$ 3,676	$ 12,276	$ 3,676
ZIOPHARM Oncology, Inc. | Preferred stock
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis				146,637		146,637		$ 129,545
Fibrocell Science, Inc.
Schedule of Investments [Line Items]
Purchases of preferred stock and warrants		$ 1,161
Fibrocell Science, Inc. | Preferred stock
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis				$ 1,862		$ 1,862