Investment in Preferred Stock - Schedule of Changes in Level 3 Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receipt of Preferred Shares as consideration for amendments to collaboration agreements	$ 120,000	$ 0	$ 0
Additional Preferred Shares received as dividend income	7,421	0	$ 0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance	0
Receipt of Preferred Shares as consideration for amendments to collaboration agreements	120,000
Additional Preferred Shares received as dividend income	7,421
Unrealized appreciation in the fair value of the investment in preferred stock	2,124
Ending balance	$ 129,545	$ 0