Investments (Details 4) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Summary of amounts included in net realized gains (losses) and other-than-temporary impairments
Balance as of January 1	$ 201,317	$ 139,766
Additions for credit impairments recognized on:
Securities not previously impaired	466	18,433
Securities previously impaired	4,933	858
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	(24,007)
Balance as of June 30	$ 182,709	$ 159,057