Commitments and Contingencies (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments And Contingencies Line Items [Abstract]
Recognized Gross losses from catastrophic events	$ 84,800,000	$ 175,500,000	$ 44,000,000
Liability related to indemnifications	8,300,000
Pretax cat loss after reinsurance	52,800,000	117,900,000	21,300,000
Letters of credit to cover obligations or anticipated payments	3,200,000
Operating Leases, Rent Expense	16,000,000	16,200,000	15,900,000
Terrorism Insurance Deductible	$ 136,500,000
Federal Reimbursement Percentage For Terrorism Losses	85.00%