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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 | Jun. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | $ 269,759 | $ 335,307
U.S. government debt securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 91,987 | 180,323
Equity securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 23,901 | 23,522
Preferred stock |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 144,742 | 129,545
Other |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 9,129 | 1,917
Quoted Prices in Active Markets (Level 1) |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 18,042 | 15,544
Quoted Prices in Active Markets (Level 1) | U.S. government debt securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Quoted Prices in Active Markets (Level 1) | Equity securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 18,042 | 15,544
Quoted Prices in Active Markets (Level 1) | Preferred stock |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Quoted Prices in Active Markets (Level 1) | Other |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Significant Other Observable Inputs (Level 2) |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 106,975 | 190,218
Significant Other Observable Inputs (Level 2) | U.S. government debt securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 91,987 | 180,323
Significant Other Observable Inputs (Level 2) | Equity securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 5,859 | 7,978
Significant Other Observable Inputs (Level 2) | Preferred stock |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Significant Other Observable Inputs (Level 2) | Other |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 9,129 | 1,917
Significant Unobservable Inputs (Level 3) |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 144,742 | 129,545
Significant Unobservable Inputs (Level 3) | U.S. government debt securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Significant Unobservable Inputs (Level 3) | Equity securities |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 0 | 0
Significant Unobservable Inputs (Level 3) | Preferred stock |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | 144,742 | 129,545
Significant Unobservable Inputs (Level 3) | Other |  |
Assets |  |
Fair value of financial assets measured at fair value on a recurring basis | $ 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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