Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Investment Holdings [Line Items]
Carrying Value	$ 747,638		$ 747,638		$ 680,638
Income (Losses) from Investment Funds	117,831	114,729	439,240	411,866
Real Estate Funds [Member]
Investment Holdings [Line Items]
Carrying Value	381,986		381,986		373,413
Energy Fund [Member]
Investment Holdings [Line Items]
Carrying Value	129,376		129,376		98,974
Arbitrage [Member]
Investment Holdings [Line Items]
Carrying Value	61,049		61,049		58,008
Other [Member]
Investment Holdings [Line Items]
Carrying Value	175,227		175,227		150,243
Investment Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			50,124	21,069
Investment Funds [Member] | Real Estate Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			13,513	14,977
Investment Funds [Member] | Energy Fund [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			28,966	10,947
Investment Funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			3,041	(2,767)
Investment Funds [Member] | Other [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			$ 4,604	$ (2,088)