Investments (Schedule Of Other Investments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	955,509		911,392
Unfunded commitments	483,214		467,524
Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	527,519		368,052
Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	427,990		543,340
Private equity (primary and secondary) | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	2 years		2 years
Private equity (primary and secondary) | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	8 years		9 years
Mezzanine debt | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	5 years		8 years
Mezzanine debt | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Distressed | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	3 years		4 years
Real estate | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years
Hedge funds | Investments without redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days
Distressed funds | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			1 year
Distressed funds | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			2 years
Distressed funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days	[1]
Equity long/short | Investments without redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days	[1]	30 days	[1]
Equity long/short | Investments without redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days	[1]	60 days	[1]
Multi-strategy | Investments without redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	45 days	[1]	45 days	[1]
Multi-strategy | Investments without redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	90 days	[1]	90 days	[1]
Event driven | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period			60 days	[1]
Relative value credit | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days	[1]	60 days	[1]
High yield loan fund | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days	[1]	30 days	[1]
Total Fair Value
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	812,543		764,081
Unfunded commitments	483,214		467,524
Total Fair Value | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	527,519		368,052
Total Fair Value | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	285,024		396,029
Total Fair Value | Private equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	357,350		216,825
Unfunded commitments	483,214		467,524
Total Fair Value | Private equity funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	357,350		216,825
Total Fair Value | Private equity funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Private equity (primary and secondary)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	184,576		144,422
Unfunded commitments	223,802		263,519
Total Fair Value | Private equity (primary and secondary) | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	184,576		144,422
Total Fair Value | Private equity (primary and secondary) | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Mezzanine debt
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	166,905		64,627
Unfunded commitments	204,232		198,756
Total Fair Value | Mezzanine debt | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	166,905		64,627
Total Fair Value | Mezzanine debt | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Distressed
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	5,869		7,776
Unfunded commitments	5,180		5,249
Total Fair Value | Distressed | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	5,869		7,776
Total Fair Value | Distressed | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Real estate
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0
Unfunded commitments	50,000
Total Fair Value | Real estate | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0
Total Fair Value | Real estate | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0
Total Fair Value | Hedge funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	425,030		515,298
Unfunded commitments	0		0
Total Fair Value | Hedge funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	170,169		151,227
Total Fair Value | Hedge funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	254,861		364,071
Total Fair Value | Distressed funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	170,169		151,227
Unfunded commitments	0		0
Total Fair Value | Distressed funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	170,169		151,227
Total Fair Value | Distressed funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Redemption frequency	Based on net asset value	[1]
Total Fair Value | Equity long/short
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	84,198		99,365
Unfunded commitments	0		0
Total Fair Value | Equity long/short | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Equity long/short | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	84,198		99,365
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value | Multi-strategy
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	51,507		136,958
Unfunded commitments	0		0
Total Fair Value | Multi-strategy | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Multi-strategy | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	51,507		136,958
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value | Event driven
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			14,018
Unfunded commitments			0
Total Fair Value | Event driven | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			0
Total Fair Value | Event driven | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			14,018
Redemption frequency			Annual	[1]
Total Fair Value | Relative value credit
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	119,156		113,730
Unfunded commitments	0		0
Total Fair Value | Relative value credit | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | Relative value credit | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	119,156		113,730
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value | High yield loan fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	30,163		31,958
Unfunded commitments	0		0
Total Fair Value | High yield loan fund | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value | High yield loan fund | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	30,163		31,958
Redemption frequency	Monthly	[1]	Monthly	[1]
Carrying Value [Member] | Other private securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	142,966		147,311
Unfunded commitments	0		0
Carrying Value [Member] | Other private securities | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Carrying Value [Member] | Other private securities | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	142,966		147,311

[1] The redemption frequency and notice periods only apply to the investments without redemption restrictions.