Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Line Items]
Gross investment income	$ 397,357	$ 439,314	$ 423,737
Less: investment expenses	(21,407)	(22,727)	(19,719)
Net investment income	375,950	416,587	404,018
Fixed maturities, available-for-sale
Net Investment Income [Line Items]
Gross investment income	242,351	269,073	262,532
Equity securities, available-for-sale:
Net Investment Income [Line Items]
Gross investment income	1	2	2
Trading account assets
Net Investment Income [Line Items]
Gross investment income	2,051	2,800	1,018
Commercial mortgage and other loans
Net Investment Income [Line Items]
Gross investment income	58,940	86,354	81,848
Policy loans
Net Investment Income [Line Items]
Gross investment income	62,735	62,304	60,847
Short-term investments and cash equivalents
Net Investment Income [Line Items]
Gross investment income	1,767	1,042	528
Other long-term investments
Net Investment Income [Line Items]
Gross investment income	$ 29,512	$ 17,739	$ 16,962

Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities.

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-16(Column G))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915

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