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Investment in Preferred Stock - Schedule of Changes in Level 3 Investments (Details) - USD ($) $ in Thousands | 12 Months Ended
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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 |

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