Reinsurance (Details 5) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Calculation of net reserves, net unearned premium and net deferred policy acquisition costs
Loss and loss adjustment expense payable	$ 3,767,850	$ 3,658,317	$ 3,471,858	$ 3,492,309
Reinsurance recoverable on outstanding losses	(479,026)	(477,760)
Reinsurance recoverable on incurred but not reported losses	(539,021)	(497,074)
Net reserves	2,749,803	2,683,483	2,537,772	2,555,840
Unearned premium	1,069,956	1,031,034
Ceded unearned premium	(256,988)	(222,300)
Net unearned premium	812,968	808,734
Deferred policy acquisition costs	191,960	189,633
Deferred ceding commissions	(74,609)	(62,364)
Net deferred policy acquisition costs	$ 117,351	$ 127,269