Significant New Business - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Aug. 06, 2012	Jul. 06, 2012 Reciprocal Of America [Member]	Sep. 30, 2012 Zurich Insurance [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Total assets and assumed total gross reinsurance reserves received	$ 16.5	$ 174.0	$ 60.0

Business combination assets and acquired and reinsurance reserves.

No definition available.

Name:	esgr_BusinessCombinationAssetsAndAcquiredAndReinsuranceReserves
Namespace Prefix:	esgr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant