SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 5) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended					1 Months Ended		1 Months Ended		1 Months Ended		0 Months Ended
	Jan. 15, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 CBIC and Rockbridge	Dec. 31, 2013 Surety segment Acquisitions prior to 2011	Apr. 30, 2011 Surety segment Contractors Bonding and Insurance Company	Dec. 31, 2013 Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty and Surety segment Contractors Bonding and Insurance Company	Dec. 31, 2013 Casualty and Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty Contractors Bonding and Insurance Company	Dec. 31, 2013 Casualty Contractors Bonding and Insurance Company	Nov. 02, 2012 Casualty Rockbridge	Dec. 31, 2013 Casualty Rockbridge	Nov. 30, 2012 Casualty Rockbridge
INTANGIBLE ASSETS
Goodwill and intangibles		$ 74,876,000				$ 76,113,000				$ 74,876,000	$ 76,113,000						$ 32,500,000						$ 16,200,000
Goodwill														26,200,000		15,100,000				5,300,000		12,400,000
Goodwill acquired															15,100,000				5,300,000		12,400,000
Indefinite Lived Intangible Assets Acquired																	8,800,000
Definite-lived intangible assets, net of amortization																		3,300,000				3,800,000
Amortization of intangible assets													1,200,000
Earnings per share:
Common stock split conversion ratio	2
Basic EPS, Income (Numerator)
Income available to common shareholders		33,859,000	37,647,000	29,902,000	24,847,000	25,097,000	25,463,000	24,748,000	28,038,000	126,255,000	103,346,000	126,598,000
Diluted EPS, Income (Numerator)
Income available to common shareholders										126,255,000	103,346,000	126,598,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding										42,744	42,431	42,156
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)										770	729	713
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding										43,514	43,160	42,869
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)		$ 0.79	$ 0.88	$ 0.70	$ 0.58	$ 0.59	$ 0.60	$ 0.58	$ 0.66	$ 2.95	$ 2.44	$ 3.00
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)		$ 0.77	$ 0.86	$ 0.69	$ 0.57	$ 0.58	$ 0.59	$ 0.58	$ 0.65	$ 2.90	$ 2.39	$ 2.95
COMPREHENSIVE EARNINGS
Tax rate used (as a percent)										35.00%	35.00%	35.00%
Other comprehensive income (loss), tax										$ (3,800,000)	$ 13,900,000	$ 11,500,000