SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended		1 Months Ended			1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 CBIC and Rockbridge	Sep. 30, 2013 CBIC and Rockbridge	Sep. 30, 2013 Surety segment Acquisitions prior to 2011	Apr. 30, 2011 Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty and Surety segment Contractors Bonding and Insurance Company	Sep. 30, 2013 Casualty and Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty Contractors Bonding and Insurance Company	Sep. 30, 2013 Casualty Rockbridge	Nov. 30, 2012 Casualty Rockbridge
INTANGIBLE ASSETS
Goodwill and intangibles	$ 75,140,000		$ 75,140,000		$ 76,113,000					$ 32,600,000				$ 16,300,000
Goodwill								26,200,000					12,400,000
Goodwill acquired									15,100,000			5,300,000
Indefinite Lived Intangible Assets Acquired										8,800,000
Impairment of assets			0
Definite-lived intangible assets, net of amortization											3,400,000		3,900,000
Amortization of intangible assets						400,000	1,000,000
Basic EPS, Income (Numerator)
Income available to common shareholders	37,647,000	25,463,000	92,396,000	78,249,000
Diluted EPS, Income (Numerator)
Income available to common shareholders	$ 37,647,000	$ 25,463,000	$ 92,396,000	$ 78,249,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,422	21,218	21,337	21,207
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)	351	268	328	312
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,773	21,486	21,665	21,519
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 1.76	$ 1.20	$ 4.33	$ 3.69
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.73	$ 1.19	$ 4.26	$ 3.64