Business Acquisition (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Jul. 02, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Assets
Short-term investments, at fair value	$ 131,936	$ 3,541	$ 57,417
Cash and cash equivalents	31,889	3,036	43,481	38,199	38,307
Premiums receivable	40,397	2,698	33,458
Deferred policy acquisition costs	26,619	1,186	24,421
Goodwill	20,983	11,666	9,317
Other assets	92,222	9,784	74,479
Total Assets	1,368,588	31,911	1,286,532	1,277,399
Liabilities:
Unpaid losses and loss adjustment expenses	683,011	(2,135)	680,201
Unearned premiums	148,993	(2,358)	135,059
Ceded premiums payable	16,808	(1,797)	11,425
Funds held	81,199	(3,504)	71,955
Other liabilities	19,634	(1,057)	14,029
Deferred income taxes	7,117	(3,060)
Total liabilities	$ 1,012,779	$ (13,911)	$ 951,852