Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Composition of deferred tax assets and liabilities
Excess of financial statement unearned premium over tax	$ 26,192	$ 26,217
Discounting of loss reserves, net of salvage and subrogation	58,105	62,402
Excess of financial statement accrued expenses over tax	18,797	16,331
Allowance for bad debts, not deductible for tax	4,733	6,216
Stock-based compensation expense in excess of deduction for tax	5,133	9,712
Financial statement loss for Lloyd's syndicates in excess of deduction for tax	0	7,571
Tax basis in net assets of foreign subsidiaries in excess of book basis	2,811	0
Federal tax net operating loss carryforwards	4,744	4,451
State tax operating loss carryforwards, net of federal tax benefit	2,631	3,352
Other items	1,142	424
Valuation allowance	9,187	7,983
Total deferred tax assets	115,101	128,693
Unrealized gain on increase in value of securities	161,098	120,854
Deferred policy acquisition costs, net of ceding commissions, deductible for tax	15,360	19,482
Amortizable goodwill for tax	97,344	84,110
Financial statement income for Lloyd's syndicates in excess of taxable income	3,860	0
Book Basis in net assets of foreign subsidiaries in excess of tax	0	10,504
Depreciation and other items	13,926	11,856
Total deferred tax liabilities	291,588	246,806
Net deferred tax liability	$ 176,487	$ 118,113