Reinsurance (Details 5) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Calculation of net reserves, net unearned premium and net deferred policy acquisition costs
Loss and loss adjustment expense payable	$ 3,658,317	$ 3,471,858	$ 3,492,309	$ 3,415,230
Reinsurance recoverable on outstanding losses	(477,760)	(452,882)
Reinsurance recoverable on incurred but not reported losses	(497,074)	(481,204)
Net reserves	2,683,483	2,537,772	2,555,840	2,416,271
Unearned premium	1,031,034	1,045,877
Ceded unearned premium	(222,300)	(278,663)
Net unearned premium	808,734	767,214
Deferred policy acquisition costs	217,608	212,786
Deferred ceding commissions	(62,364)	(72,565)
Net deferred policy acquisition costs	$ 155,244	$ 140,221