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Investments (Credit Concentration Risk) (Details)	Jun. 30, 2018	Dec. 31, 2017
Investments [Abstract]
Maximum exposure to credit concentration risk of the Company's stockholder's equity other than certain U.S. government agencies	10.00%	10.00%

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- Definition

Maximum exposure to credit concentration risk of the Company's stockholder's equity other than certain U.S. government agencies

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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