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Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy) (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Carrying Value		$ 182,109	$ 178,938
Other Investments [Member]
Carrying Value		182,109	178,938
Remaining Commitment		231,818	202,270
Maximum Exposure to Loss	[1]	413,927	381,208
Alternative Investments [Member]
Carrying Value		157,774	153,896
Remaining Commitment		231,818	202,270
Maximum Exposure to Loss	[1]	389,592	356,166
Private Equity [Member] | Alternative Investments [Member]
Carrying Value		99,567	84,352
Remaining Commitment		95,805	93,688
Maximum Exposure to Loss	[1]	195,372	178,040
Private Credit [Member] | Alternative Investments [Member]
Carrying Value		35,103	41,682
Remaining Commitment		113,133	81,453
Maximum Exposure to Loss	[1]	148,236	123,135
Real Assets [Member] | Alternative Investments [Member]
Carrying Value		23,104	27,862
Remaining Commitment		22,880	27,129
Maximum Exposure to Loss	[1]	45,984	54,991
Other Securities [Member]
Carrying Value		24,335	25,042
Remaining Commitment		0	0
Maximum Exposure to Loss	[1]	$ 24,335	$ 25,042
[1] The maximum exposure to loss includes both the carry value of these investments and the related remaining commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant.

X

- Definition

This item represents contractual obligations to invest additional amounts on our other investment portfolio. These additional investments may or may not be required.

+ References

No definition available.

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- Definition

Amount of investments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5747-111685

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5728-111685

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