SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended		1 Months Ended			1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 CBIC and Rockbridge	Jun. 30, 2013 CBIC and Rockbridge	Jun. 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	Jun. 30, 2013 Casualty and Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty Contractors Bonding and Insurance Company	Jun. 30, 2013 Casualty Rockbridge	Nov. 30, 2012 Casualty Rockbridge
INTANGIBLE ASSETS
Goodwill and intangibles	$ 75,463,000		$ 75,463,000		$ 76,113,000					$ 32,900,000				$ 16,400,000
Goodwill								26,200,000					12,400,000
Goodwill acquired									15,100,000			5,300,000
Indefinite Lived Intangible Assets											8,800,000
Indefinite Lived Intangible Assets Acquired										8,800,000
Impairment of assets			0
Definite-lived intangible assets, net of amortization											3,700,000		4,000,000
Amortization of intangible assets						300,000	600,000
Basic EPS, Income (Numerator)
Income available to common shareholders	29,902,000	24,748,000	54,749,000	52,786,000
Diluted EPS, Income (Numerator)
Income available to common shareholders	$ 29,902,000	$ 24,748,000	$ 54,749,000	$ 52,786,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,314	21,213	21,293	21,200
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)	356	301	341	321
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,670	21,514	21,634	21,521
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 1.40	$ 1.17	$ 2.57	$ 2.49
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.38	$ 1.15	$ 2.53	$ 2.45