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Marketable Securities - Available-For-Sale Securities (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract] |  |  |
Available-for-sale securities, other than temporary impairment losses | $ 0 | $ 0 |
Interest Income, Other | $ 2,300,000 | $ 2,400,000 | $ 2,300,000

X
- Definition Amount of interest income earned from interest bearing assets classified as other. + References No definition available. + Details
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- Definition The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References No definition available. + Details
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