Liability for Unpaid Loss and Loss Adjustment Expenses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of activity in the liability for unpaid loss and loss adjustment expenses
Unpaid loss and loss adjustment expenses, Beginning balance	$ 680,201	$ 649,641	$ 616,444
Reinsurance recoverable on unpaid losses and loss adjustment expenses, Beginning Balance	173,982	196,590	196,080
Net unpaid loss and loss adjustment expenses, Beginning balance	506,934	453,051	420,364
Incurred related to:
Current year	162,660	155,998	119,939
Prior years	9,038	13,369	356
Total incurred	171,698	169,367	120,295
Paid related to:
Current year	26,822	22,454	13,302
Prior years	112,214	93,030	74,306
Total paid	139,036	115,484	87,608
Net unpaid loss and loss adjustment expenses, Ending balance	539,596	506,934	453,051
Reinsurance recoverable on unpaid loss and loss adjustment expenses, Ending Balance	183,562	173,982	196,590
Unpaid loss and loss adjustment expenses, Ending balance	$ 725,244	$ 680,201	$ 649,641