Statutory Requirements (Statutory Capital and Surplus) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Bermuda
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 5,325,749	$ 4,366,089
Required statutory capital and surplus	1,201,529	957,650
Unrestricted net assets	1,107,586	931,387
Switzerland
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	580,235	0
Required statutory capital and surplus	465,900	0
Unrestricted net assets	102,943	0
U.S.
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	677,832	502,803
Required statutory capital and surplus	397,447	306,628
Unrestricted net assets	46,630	31,228
U.K.
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	675,864	519,689
Required statutory capital and surplus	675,864	519,689
Unrestricted net assets	$ 0	$ 0

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- Definition

Amount of dividends that can be declared or paid without approval of regulatory agency.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ 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(a)(23)(c))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

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- Definition

Amount of statutory capital required to be maintained as of the balance sheet date under prescribed or permitted statutory accounting practices.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

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