Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Composition of deferred tax assets and liabilities
Excess of financial statement unearned premium over tax	$ 26,217	$ 22,897
Discounting of loss reserves, net of salvage and subrogation	62,402	61,738
Excess of financial statement accrued expenses over tax	17,373	22,635
Allowance for bad debts, not deductible for tax	6,216	5,721
Stock-based compensation expense in excess of deduction for tax	9,712	12,339
Financial statement loss for syndicate in excess of deduction for tax	7,571	0
Federal tax net operating loss carryforwards	4,451	3,859
State tax operating loss carryforwards, net of federal tax benefit	2,179	2,205
Other items	424	211
Valuation allowance	7,607	7,767
Total deferred tax assets	128,938	123,838
Unrealized gain on increase in value of securities	120,854	48,656
Deferred policy acquisition costs, net of ceding commissions, deductible for tax	29,271	21,244
Amortizable goodwill for tax	84,110	72,252
Book Basis in net assets of foreign subsidiaries in excess of tax	10,903	8,295
Property and equipement depreciation and other items	11,856	11,322
Total deferred tax liabilities	256,994	161,769
Net deferred tax liability	$ 128,056	$ 37,931