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Fair Value Measurements - Summary of Placement in the Fair Value Hierarchy of Financial Assets that are Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Assets |  |
Fair value of assets | $ 335,307 | $ 291,762
US government debt securities |  |
Assets |  |
Fair value of assets | 180,323 | 207,704
Equity securities |  |
Assets |  |
Fair value of assets | 23,522 | 83,653
Preferred stock |  |
Assets |  |
Fair value of assets | 129,545 |
Other |  |
Assets |  |
Fair value of assets | 1,917 | 405
Quoted Prices in Active Markets (Level 1) |  |
Assets |  |
Fair value of assets | 15,544 | 65,850
Quoted Prices in Active Markets (Level 1) | US government debt securities |  |
Assets |  |
Fair value of assets | 0 | 0
Quoted Prices in Active Markets (Level 1) | Equity securities |  |
Assets |  |
Fair value of assets | 15,544 | 65,850
Quoted Prices in Active Markets (Level 1) | Preferred stock |  |
Assets |  |
Fair value of assets | 0 |
Quoted Prices in Active Markets (Level 1) | Other |  |
Assets |  |
Fair value of assets | 0 | 0
Significant Other Observable Inputs (Level 2) |  |
Assets |  |
Fair value of assets | 190,218 | 225,912
Significant Other Observable Inputs (Level 2) | US government debt securities |  |
Assets |  |
Fair value of assets | 180,323 | 207,704
Significant Other Observable Inputs (Level 2) | Equity securities |  |
Assets |  |
Fair value of assets | 7,978 | 17,803
Significant Other Observable Inputs (Level 2) | Preferred stock |  |
Assets |  |
Fair value of assets | 0 |
Significant Other Observable Inputs (Level 2) | Other |  |
Assets |  |
Fair value of assets | 1,917 | 405
Significant Unobservable Inputs (Level 3) |  |
Assets |  |
Fair value of assets | 129,545 | 0
Significant Unobservable Inputs (Level 3) | US government debt securities |  |
Assets |  |
Fair value of assets | 0 | 0
Significant Unobservable Inputs (Level 3) | Equity securities |  |
Assets |  |
Fair value of assets | 0 | 0
Significant Unobservable Inputs (Level 3) | Preferred stock |  |
Assets |  |
Fair value of assets | 129,545 |
Significant Unobservable Inputs (Level 3) | Other |  |
Assets |  |
Fair value of assets | $ 0 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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