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		3 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 CBIC and Rockbridge	Sep. 30, 2014 CBIC and Rockbridge	Sep. 30, 2014 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, 2014 Casualty and Surety segment Contractors Bonding and Insurance Company	Sep. 30, 2014 Casualty and Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty segment Contractors Bonding and Insurance Company	Sep. 30, 2013 Casualty segment Rockbridge	Sep. 30, 2014 Casualty segment Rockbridge
INTANGIBLE ASSETS
Goodwill and intangibles	$ 74,172,000		$ 74,172,000		$ 74,876,000						$ 32,000,000	$ 32,000,000			$ 16,000,000
Goodwill								26,200,000							12,400,000
Goodwill acquired									15,100,000				5,300,000
Indefinite Lived Intangible Assets Acquired										8,800,000
Goodwill, Impairment Loss											0	0		0
Impairment of indefinite-lived intangible assets											0	0
Definite-lived intangible assets, net of amortization											2,800,000	2,800,000			3,600,000
Amortization of intangible assets						200,000	700,000
Basic EPS, Income (Numerator)
Income available to common shareholders	33,254,000	37,647,000	97,948,000	92,396,000
Diluted EPS, Income (Numerator)
Income available to common shareholders	$ 33,254,000	$ 37,647,000	$ 97,948,000	$ 92,396,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	43,026	42,843	43,004	42,673
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)	686	703	688	657
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	43,712	43,546	43,692	43,330
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 0.77	$ 0.88	$ 2.28	$ 2.17
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 0.76	$ 0.86	$ 2.24	$ 2.13