Net Investment Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net Investment Income [Line Items]
Investment income	$ 145,519	$ 162,691	$ 283,460	$ 321,409
Investment expense	(1,782)	(1,441)	(3,794)	(2,540)
Net investment income	143,737	161,250	279,666	318,869
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Investment income	111,203	119,835	229,039	239,123
Investment funds
Net Investment Income [Line Items]
Investment income	22,576	35,619	33,510	63,242
Arbitrage trading account
Net Investment Income [Line Items]
Investment income	4,990	60	8,773	6,541
Equity securities available for sale
Net Investment Income [Line Items]
Investment income	3,634	3,829	5,881	6,979
Real estate
Net Investment Income [Line Items]
Investment income	$ 3,116	$ 3,348	$ 6,257	$ 5,524