Investment in Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis		$ 376,093	$ 376,093		$ 291,762
Noncash dividend income on preferred shares			3,676	$ 0
Preferred stock
Schedule of Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis		$ 123,676	$ 123,676
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Preferred shares, stated value (in usd per share)	$ 1,200
Threshold consecutive trading days, conversion of shares			20 days
Preferred shares, dividend rate (in usd per share)			$ 12.00
Preferred shares, dividend rate, for unconverted shares after conversion event (in usd per share)			24.00
ZIOPHARM Oncology, Inc. | Minimum
Schedule of Investments [Line Items]
Preferred shares, conversion calculation, divisor (in usd per share)			$ 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)	100,000
ZIOPHARM Oncology, Inc.
Schedule of Investments [Line Items]
Dividend income, number of preferred shares received (in shares)		3,063	3,063
Noncash dividend income on preferred shares		$ 3,676	$ 3,676