Investment Funds Investment Funds (Schedule of Investment Funds) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment Holdings [Line Items]
Investment funds	$ 680,638	$ 512,411
Gross investment income	529,820	534,085	382,596
Real estate [Member]
Investment Holdings [Line Items]
Investment funds	373,413	226,183
Energy [Member]
Investment Holdings [Line Items]
Investment funds	98,974	96,511
Arbitrage [Member]
Investment Holdings [Line Items]
Investment funds	58,008	60,660
Other [Member]
Investment Holdings [Line Items]
Investment funds	150,243	129,057
Investment funds [Member]
Investment Holdings [Line Items]
Gross investment income	9,452	(6,481)	(163,862)
Investment funds [Member] | Real estate [Member]
Investment Holdings [Line Items]
Gross investment income	14,527	(4,766)	(159,569)
Investment funds [Member] | Energy [Member]
Investment Holdings [Line Items]
Gross investment income	(6,101)	996	(13,227)
Investment funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Gross investment income	(1,366)	1,692	9,691
Investment funds [Member] | Other [Member]
Investment Holdings [Line Items]
Gross investment income	$ 2,392	$ (4,403)	$ (757)