Reserve For Losses, LAE And Future Policy Benefit Reserve (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jul. 13, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Increase (decrease) in insurance business		$ (68,567)	$ (39,862)	$ (18,239)
Increase (decrease) in reinsurance business		217,169	(202,418)	(148,788)
Reinsurance receivables		$ 840,420	670,854
Retrocession percent		5.00%
Contracts of insurance and reinsurance received claims during the past three years, in years		20 years
Case reserve established by the Company on direct excess insurance claims		$ 9,951,798	9,720,813	9,673,240	$ 10,069,055
Liabilites retroceded, percentage	100.00%
Cash conisderation	$ 140,279
Maximum liability retroceded	440,279
Total amount of liabilities retroceded	300,000
Construction Liability, Umbrella, and Workers Compenstion Reserves [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Increase (decrease) in insurance business		152,140	24,973	$ 130,548
Resolution Group Reinsurance (Barbados) Limited [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 194,231
Reinsurance receivable, percent		23.10%
Zurich Vericherungs Gesellschaft [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 88,136
Reinsurance receivable, percent		10.50%
C. V. Starr [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 104,819
Reinsurance receivable, percent		12.50%
Transatlantic Reinsurance Company [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 43,992
Reinsurance receivable, percent		5.20%
Hannover Rueck SE [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 46,588
Reinsurance receivable, percent		5.50%
Axis Reinsurance Company [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Reinsurance receivables		$ 49,478
Reinsurance receivable, percent		5.90%
A&E [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Partially offset, related to development on A&E reserves			(137,769)
Cash conisderation	$ 100,451
Mt. Logan Re [Member]
Reserve For Losses LAE And Future Policy Benefit Reserve [Line Items]
Partially offset, related to development on A&E reserves		$ 3,539	$ 186