Reinsurances (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 249,810	$ 241,428	$ 231,419
Ceded to Other Companies	56,700	59,596	71,558
Assumed from Other Companies	60,756	51,047	40,872
Net Amount	253,866	232,879	200,733
Percentage of Amount Assumed to Net	23.90%	21.90%	20.40%
United States [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	249,810	241,428	231,419
Ceded to Other Companies	56,700	59,596	71,558
Net Amount	193,110	181,832	159,861
Bermuda [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Assumed from Other Companies	60,756	51,047	40,872
Net Amount	$ 60,756	$ 51,047	$ 40,872
Percentage of Amount Assumed to Net	100.00%	100.00%	100.00%