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			3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Casualty	Jun. 30, 2011 Casualty	Jun. 30, 2012 Casualty	Jun. 30, 2011 Casualty	Jun. 30, 2012 Surety	Jun. 30, 2011 Surety	Jun. 30, 2012 Surety	Jun. 30, 2011 Surety	Jun. 30, 2012 Contractors Bonding and Insurance Company office	Jun. 30, 2012 Contractors Bonding and Insurance Company Y office	Apr. 28, 2011 Contractors Bonding and Insurance Company	Jun. 30, 2012 Contractors Bonding and Insurance Company Minimum person	Jun. 30, 2012 Contractors Bonding and Insurance Company Casualty	Jun. 30, 2012 Contractors Bonding and Insurance Company Surety
Business acquisition
Business acquisition consideration paid in cash															$ 135,900,000
Number of contractors served by the acquiree																30,000
Number of regional branch offices operated by the acquiree													12	12
Number of insurance agents and brokers served by the acquiree																4,000
Amount of goodwill resulting from acquisition															20,400,000
Amount of separately identifiable intangible assets resulting from acquisition															14,500,000
Amount of separately identifiable intangible assets resulting from acquisition, net of related amortization													13,400,000	13,400,000
Business acquisition purchase accounting adjustments, maximum tenure (in years)														1
Premiums written													14,700,000				9,000,000	5,700,000
Pretax earnings contributed													6,400,000
Underwriting income	21,623,000	42,090,000	36,564,000	63,037,000	11,051,000	25,844,000	11,603,000	31,381,000	10,862,000	8,814,000	13,334,000	14,191,000	5,300,000	4,800,000
Net investment income													1,100,000	2,100,000
Valuation of insurance policies in force, including value of business acquired													1,000,000	1,000,000	10,800,000
Unearned premium (UEP) acquired													1,900,000	1,900,000	29,500,000
Percentage of unearned premium (UEP) acquired earned as revenue													93.00%	93.00%
Favorable reserve development on prior years' loss reserves													$ 6,500,000	$ 6,500,000