Investments (Details) - Analysis of net realized gains (losses) and the change in unrealized (losses) gains on investments (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net realized gains (losses):
Total net realized gains (losses) on investments	$ 14,098	$ (188,359)	$ (270,803)
Net realized and unrealized (losses) on investment related derivative instruments	(1,228)	(22,981)	(16,321)
Net realized (losses) on investments and net realized and unrealized (losses) on investment related derivative instruments	12,870	(211,340)	(287,124)
Net change in unrealized gains (losses) on investments	1,196,430	795,712	1,192,710
Total net realized (losses) on investments, net realized and unrealized (losses) on investment related derivative instruments, and net change in unrealized gains (losses) on investments	1,209,300	584,372	905,586
Fixed maturities, short term investments and cash equivalents
Net realized gains (losses):
Gross realized gains	163,328	185,530	133,521
Gross realized losses on investments sold	(107,033)	(225,360)	(193,396)
OTTI on investments, net of amounts transferred to other comprehensive income	(74,245)	(159,435)	(197,377)
Total net realized gains (losses) on investments	(17,950)	(199,265)	(257,252)
Fixed maturities | AFS
Net realized gains (losses):
Net change in unrealized gains (losses) on investments	884,259	598,542	1,095,762
Fixed maturities | HTM
Net realized gains (losses):
Net change in unrealized gains (losses) on investments	221,647	212,419	30,039
Equity securities
Net realized gains (losses):
Gross realized gains	42,009	2,194	11,605
Gross realized losses on investments sold	(7,121)	(4,264)	(11,195)
OTTI on investments, net of amounts transferred to other comprehensive income	(3,746)	0	0
Total net realized gains (losses) on investments	31,142	(2,070)	410
Net change in unrealized gains (losses) on investments	44,361	(40,518)	22,595
Other investments
Net realized gains (losses):
Gross realized gains	11,610	18,505	4,889
Gross realized losses on investments sold	(7,983)	(4,792)	(11,094)
OTTI on investments, net of amounts transferred to other comprehensive income	(2,721)	(737)	(7,756)
Total net realized gains (losses) on investments	906	12,976	(13,961)
Affiliates and other investments
Net realized gains (losses):
Net change in unrealized gains (losses) on investments	$ 46,163	$ 25,269	$ 44,314