The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 4
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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Investments (Mortgage Loans by Method of Evaluation and Related Valuation Allowances) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Mortgage Loans:
Recorded investment	$ 4,450,291	$ 4,413,171
Valuation Allowances:
Allowance for Loan and Lease Losses, Real Estate	8,864	9,384	$ 7,786	$ 7,685
Commercial Real Estate Portfolio Segment [Member]
Mortgage Loans:
Evaluated individually for credit losses	23,423	5,858
Evaluated collectively for credit losses	4,426,868	4,407,313
Recorded investment	4,450,291	4,413,171
Valuation Allowances:
Specific for credit losses	0	0
Non-specifically identified credit losses	8,864	9,384
Allowance for Loan and Lease Losses, Real Estate	$ 8,864	$ 9,384