Reserve for Claims and Claim Expenses (Schedule of Liability for Unpaid Claims and Claims Adjustment Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves as of January 1	$ 1,462,705	$ 1,686,865	$ 1,588,325
Net incurred related to:
Current year	341,745	315,241	483,180
Prior years	(143,798)	(143,954)	(157,969)
Total net incurred	197,947	171,287	325,211
Net paid related to:
Current year	39,830	32,212	84,056
Prior years	275,006	363,235	142,615
Total net paid	314,836	395,447	226,671
Net reserves as of December 31	1,345,816	1,462,705	1,686,865
Reinsurance recoverable as of December 31	66,694us-gaap_ReinsuranceRecoverables	101,025us-gaap_ReinsuranceRecoverables	192,512us-gaap_ReinsuranceRecoverables
Gross reserves as of December 31	1,412,510	1,563,730	1,879,377
Catastrophe Reinsurance
Net incurred related to:
Current year	67,268	109,945	275,777
Prior years	(65,511)	(102,037)	(110,568)
Total net incurred	1,757	7,908	165,209
Specialty Reinsurance
Net incurred related to:
Current year	144,411	101,347	110,959
Prior years	(55,909)	(34,111)	(34,146)
Total net incurred	88,502	67,236	76,813
Lloyd's
Net incurred related to:
Current year	130,066	103,949	96,444
Prior years	(16,241)	(8,256)	(16,202)
Total net incurred	113,825	95,693	80,242
Other
Net incurred related to:
Current year	0	0	0
Prior years	(6,137)	450	2,947
Total net incurred	$ (6,137)	$ 450	$ 2,947

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

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Amount of payments to settle claims incurred in the current period and related claims settlement costs.

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Amount of payments to settle claims incurred in prior periods and related claims settlement costs.

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Amount of expense for claims incurred and costs incurred in the claim settlement process.

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Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.

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Amount of payments to settle insured claims and pay costs incurred in the claims settlement process.

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Amount after valuation allowance recoverable including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

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Amount of expense for claims incurred in the current reporting period and related claims settlement costs.

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Amount of expense for claims incurred in prior reporting periods and related claims settlement costs.

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