Summary of Significant Accounting Policies - Equity Method Investments - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	$ 269,759		$ 269,759		$ 335,307
Oragenics, Inc.
Schedule of Equity Method Investments [Line Items]
Company's ownership percentage	29.40%		29.40%		29.50%
Equity securities
Schedule of Equity Method Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	$ 23,901		$ 23,901		$ 23,522
Equity securities | Oragenics, Inc.
Schedule of Equity Method Investments [Line Items]
Fair value of financial assets measured at fair value on a recurring basis	4,807		4,807		$ 7,244
Unrealized depreciation in fair value of equity securities	$ (1,096)	$ (4,797)	$ (2,437)	$ (11,142)