Statutory Financial Information (Actual Statutory Capital And Surplus) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
United States [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	$ 3,158,828	$ 3,424,330
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	621,802	642,418
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	1,495,563	1,779,387
Other Countries [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	$ 74,704	$ 34,002

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.

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=6879938&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

Name:	us-gaap_StatutoryAccountingPracticesStatutoryCapitalAndSurplusBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant