Investments (Schedule Of Other Investments) (Details) (USD $) In Thousands, unless otherwise specified										9 Months Ended				9 Months Ended				9 Months Ended					9 Months Ended			9 Months Ended									9 Months Ended								9 Months Ended									9 Months Ended				9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Investments with redemption restrictions [Member]	Sep. 30, 2012 Investments without redemption restrictions [Member]	Sep. 30, 2012 Private Equity Funds [Member]	Sep. 30, 2012 Private Equity Funds [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Private Equity Funds [Member] Investments without redemption restrictions [Member]	Sep. 30, 2012 Private Equity (Primary And Secondary) [Member]	Sep. 30, 2012 Private Equity (Primary And Secondary) [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Private Equity (Primary And Secondary) [Member] Investments with redemption restrictions [Member] Minimum [Member]	Sep. 30, 2012 Private Equity (Primary And Secondary) [Member] Investments with redemption restrictions [Member] Maximum [Member]	Sep. 30, 2012 Private Equity (Primary And Secondary) [Member] Investments without redemption restrictions [Member]	Sep. 30, 2012 Mezzanine Debt [Member]	Sep. 30, 2012 Mezzanine Debt [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Mezzanine Debt [Member] Investments without redemption restrictions [Member]	Sep. 30, 2012 Distressed [Member]	Sep. 30, 2012 Distressed [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Distressed [Member] Investments with redemption restrictions [Member] Maximum [Member]	Sep. 30, 2012 Distressed [Member] Investments without redemption restrictions [Member]	Sep. 30, 2012 Hedge Funds [Member]	Sep. 30, 2012 Hedge Funds [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Hedge Funds [Member] Investments without redemption restrictions [Member]	Sep. 30, 2012 Hedge Funds [Member] Investments without redemption restrictions [Member] Minimum [Member]	Sep. 30, 2012 Distressed Funds [Member]	Sep. 30, 2012 Distressed Funds [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Distressed Funds [Member] Investments with redemption restrictions [Member] Maximum [Member]	Sep. 30, 2012 Distressed Funds [Member] Investments without redemption restrictions [Member]		Sep. 30, 2012 Distressed Funds [Member] Investments without redemption restrictions [Member] Minimum [Member]		Sep. 30, 2012 Distressed Funds [Member] Investments without redemption restrictions [Member] Maximum [Member]		Sep. 30, 2012 Equity Long/Short [Member]	Sep. 30, 2012 Equity Long/Short [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Equity Long/Short [Member] Investments without redemption restrictions [Member]		Sep. 30, 2012 Equity Long/Short [Member] Investments without redemption restrictions [Member] Minimum [Member]		Sep. 30, 2012 Equity Long/Short [Member] Investments without redemption restrictions [Member] Maximum [Member]		Sep. 30, 2012 Multi-Strategy Funds [Member]	Sep. 30, 2012 Multi-Strategy Funds [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Multi-Strategy Funds [Member] Investments with redemption restrictions [Member] Maximum [Member]	Sep. 30, 2012 Multi-Strategy Funds [Member] Investments without redemption restrictions [Member]		Sep. 30, 2012 Multi-Strategy Funds [Member] Investments without redemption restrictions [Member] Minimum [Member]		Sep. 30, 2012 Multi-Strategy Funds [Member] Investments without redemption restrictions [Member] Maximum [Member]		Sep. 30, 2012 Global Macro [Member]	Sep. 30, 2012 Global Macro [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Global Macro [Member] Investments without redemption restrictions [Member]		Sep. 30, 2012 Event Driven Funds [Member]	Sep. 30, 2012 Event Driven Funds [Member] Investments with redemption restrictions [Member]	Sep. 30, 2012 Event Driven Funds [Member] Investments without redemption restrictions [Member]		Sep. 30, 2012 Event Driven Funds [Member] Investments without redemption restrictions [Member] Minimum [Member]		Sep. 30, 2012 Event Driven Funds [Member] Investments without redemption restrictions [Member] Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets trading, at fair value	$ 564,702	$ 540,409	$ 151,363	$ 413,339	$ 124,195	$ 124,195	$ 0	$ 87,241	$ 87,241			$ 0	$ 27,444	$ 27,444	$ 0	$ 9,510	$ 9,510		$ 0	$ 440,507	$ 27,168	$ 413,339		$ 42,248	$ 212		$ 42,036						$ 170,023	$ 0	$ 170,023						$ 140,141	$ 26,956		$ 113,185						$ 19,246	$ 0	$ 19,246		$ 68,849	$ 0	$ 68,849
Estimated remaining restriction period										4 years	10 years			10 years				6 years								2 years																	2 years
Redemption frequency																											Quarterly	[1]							Quarterly	[1]								Quarterly	[1]							Monthly	[1]			Annual	[1]
Required notification period for redemption																							P30D						P45D	[1]	P65D	[1]					P30D	[1]	P60D	[1]						P45D	[1]	P90D	[1]			P3D	[1]					P45D	[1]	P60D	[1]
Unfunded Commitments	$ 255,929				$ 255,929			$ 158,129					$ 89,000			$ 8,800				$ 0				$ 0									$ 0								$ 0									$ 0				$ 0

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