Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill and Intangible Assets - Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	May 14, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill	$ 114,807,000	$ 114,807,000		$ 73,071,000
Impairment of goodwill	0
Non-life Run-off
Segment Reporting Information [Line Items]
Goodwill	62,959,000	62,959,000
Atrium Segment
Segment Reporting Information [Line Items]
Goodwill	38,848,000	38,848,000
StarStone
Segment Reporting Information [Line Items]
Goodwill	$ 13,000,000	$ 13,000,000
KaylaRe
Segment Reporting Information [Line Items]
Goodwill			$ 41,736,000