Net Investment Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Jun. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Investment Income [Line Items]
Investment income	$ 127,541	$ 117,831	$ 411,001	$ 439,240
Investment expense	(1,907)	(1,812)	(5,701)	(4,352)
Net investment income	125,634	116,019	405,300	434,888
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Investment income	104,033	121,454	333,072	360,577
Investment funds
Net Investment Income [Line Items]
Investment income	5,492	(13,118)	45,248	50,124
Arbitrage trading account
Net Investment Income [Line Items]
Investment income	11,738	2,397	14,265	8,938
Equity securities available for sale
Net Investment Income [Line Items]
Investment income	3,192	4,001	9,073	10,980
Real estate
Net Investment Income [Line Items]
Investment income	$ 3,086	$ 3,097	$ 9,343	$ 8,621