SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Goodwill
Goodwill and intangibles	$ 60,248,000		$ 60,482,000
Amortization of intangible assets	300,000
Basic EPS, Income (Numerator)
Income available to common shareholders	28,038,000	27,706,000
Diluted EPS, Income (Numerator)
Income available to common shareholders	28,038,000	27,706,000
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,188	21,025
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding	21,528	21,285
Basic EPS, Per Share Amount
Basic earnings per share (in dollars per share)	$ 1.32	$ 1.32
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.30	$ 1.30
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)	340	260
Surety segment
Goodwill
Goodwill	26,200,000		26,200,000
Casualty and Surety segment | Contractors Bonding and Insurance Company
Goodwill
Goodwill and intangibles	$ 34,000,000