Fair Value (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Fair Value Measurements [Line Items]
Investments measured at net asset value based on an ownership interest in partners'	2.00%	2.00%	2.00%
Transfer between Level 2 and Level 3	$ 0	$ 0
Fair Value Measured Using NAV [Member] \| Limited Partnerships Interest [Member]
Fair Value Measurements [Line Items]
Investments measured at fair value using net asset value	161,100,000	161,100,000	$ 172,800,000
Level 3 [Member]
Fair Value Measurements [Line Items]
Investments measured at fair value using net asset value	4,000,000.0	4,000,000.0	$ 4,000,000.0
Liabilities held	$ 0	$ 0		$ 0

Fair Value Measurements [Line Items]

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- Definition

Fair value transfers between level 2 and level 3 amount.

+ References

No definition available.

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- Definition

Percentage Of Investments Not Included In Fair Value Of Financial Instruments

+ References

No definition available.

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- Definition

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 35
-Paragraph 54B
-URI http://asc.fasb.org/extlink&oid=117332851&loc=SL7495116-110257

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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