ACQUISITION (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Contractors Bonding and Insurance Company (CBIC)	Jun. 30, 2011 Contractors Bonding and Insurance Company (CBIC)	Apr. 28, 2011 Contractors Bonding and Insurance Company (CBIC)	Jun. 30, 2011 Casualty	Jun. 30, 2010 Casualty	Jun. 30, 2011 Casualty	Jun. 30, 2010 Casualty	Jun. 30, 2011 Surety	Jun. 30, 2010 Surety	Jun. 30, 2011 Surety	Jun. 30, 2010 Surety	Jun. 30, 2011 Corporates	Jun. 30, 2011 Equity
Business acquisition
Business acquisition consideration paid in cash							$ 135,900,000
Number of contractors served by the acquiree					30,000	30,000
Number of insurance agents and brokers served by the acquiree					4,000	4,000
Number of regional branch offices operated by the acquiree					13	13
Amount of goodwill resulting from acquisition					19,700,000	19,700,000
Amount of separately identifiable intangible assets resulting from acquisition					10,600,000	10,600,000
Business acquisition purchase accounting adjustments, maximum tenure (in years)						1
Business acquisition gross premium written					10,300,000
Premiums written								5,800,000				4,500,000
Underwriting income (loss)	45,765,000	30,801,000	64,797,000	43,516,000	(200,000)			26,920,000	13,594,000	31,594,000	14,208,000	9,678,000	7,873,000	14,655,000	11,927,000
Net investment income					$ 300,000
Percentage of investments sold (as a percent)																60.00%	24.00%