Ceded Reinsurance (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Concentration Risk [Line Items]
Impact of Commutation on ceded premiums written and earned		$ 12,393	$ 9,296
Commutation of variable-rated reinsurance contracts	$ 0	$ 11,529	$ 8,864
Percentage of reinsurance recoverable	100.00%	100.00%
Credit Concentration Risk [Member] | Premiums Ceded [Member]
Concentration Risk [Line Items]
Number of ceded reinsurers	4	4	4
Gross written premium, percentage	48.00%	54.00%	56.00%
Credit Concentration Risk [Member] | Reinsurance Recoverable [Member] | A- or better rating
Concentration Risk [Line Items]
Percentage of reinsurance recoverable	99.00%	99.00%