Reinsurance (Details 5) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Calculation of net reserves, net unearned premium and net deferred policy acquisition costs
Loss and loss adjustment expense payable	$ 3,755,699	$ 3,658,317
Reinsurance recoverable on outstanding losses	(518,288)	(477,760)
Reinsurance recoverable on incurred but not reported losses	(488,416)	(497,074)
Net reserves	2,748,995	2,683,483
Unearned premium	1,147,121	1,031,034
Ceded unearned premium	(255,078)	(222,300)
Net unearned premium	892,043	808,734
Deferred policy acquisition costs	204,387	189,633
Deferred ceding commissions	(71,767)	(62,364)
Net deferred policy acquisition costs	$ 132,620	$ 127,269