SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended					1 Months Ended		1 Months Ended		1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Surety segment	Dec. 31, 2011 Surety segment	Apr. 30, 2011 Surety segment Contractors Bonding and Insurance Company	Sep. 30, 2012 Surety segment Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty Contractors Bonding and Insurance Company	Sep. 30, 2012 Casualty Contractors Bonding and Insurance Company	Apr. 30, 2011 Casualty and Surety segment Contractors Bonding and Insurance Company	Sep. 30, 2012 Casualty and Surety segment Contractors Bonding and Insurance Company
Goodwill
Goodwill						$ 26,200,000	$ 26,200,000		$ 15,100,000		$ 5,300,000
Goodwill acquired								15,100,000		5,300,000
Indefinite Lived Intangible Assets													8,800,000
Indefinite Lived Intangible Assets Acquired												8,800,000
Goodwill and intangibles	59,780,000		59,780,000		60,482,000								33,600,000
Amortization of intangible assets	200,000		700,000
Basic EPS, Income (Numerator)
Income available to common shareholders	25,463,000	23,969,000	78,249,000	96,667,000
Diluted EPS, Income (Numerator)
Income available to common shareholders	$ 25,463,000	$ 23,969,000	$ 78,249,000	$ 96,667,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,218	21,089	21,207	21,063
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,486	21,335	21,519	21,324
Basic EPS, Per Share Amount
Basic earnings per share (in dollars per share)	$ 1.20	$ 1.14	$ 3.69	$ 4.59
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.19	$ 1.12	$ 3.64	$ 4.53
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)	268	246	312	261