SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Intangible Assets and EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
INTANGIBLE ASSETS
Goodwill		$ 51,270			$ 51,270		$ 58,496
Definite-lived intangibles, net of accumulated amortization of $5,339 at 9/30/16 and $4,678 at 12/31/15		5,808			5,808		5,298
Total intangibles		13,308			13,308		12,798
Goodwill and intangibles		64,578			64,578		71,294
Accumulated amortization of definite-lived intangibles		5,339			5,339		4,678
Amortization of intangible assets		200		$ 200	700	$ 700
Finite-lived Intangible Assets Acquired					1,200
Basic EPS, Income (Numerator)
Income available to common shareholders		22,263		35,908	82,733	103,691
Diluted EPS, Income (Numerator)
Income available to common shareholders		$ 22,263		$ 35,908	$ 82,733	$ 103,691
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding		43,843		43,342	43,721	43,232
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)		649		811	695	799
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding		44,492		44,153	44,416	44,031
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)		$ 0.51		$ 0.83	$ 1.89	$ 2.40
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)		$ 0.50		$ 0.81	$ 1.86	$ 2.35
Contractors Bonding and Insurance Company
INTANGIBLE ASSETS
State insurance licenses		$ 7,500			$ 7,500		7,500
Energy Surety
INTANGIBLE ASSETS
Goodwill		25,706			25,706		25,706
Miscellaneous and Contract Surety
INTANGIBLE ASSETS
Goodwill		15,110			15,110		15,110
P&C package business
INTANGIBLE ASSETS
Goodwill		5,246			5,246		5,246
Medical professional liability
INTANGIBLE ASSETS
Goodwill	[1]	5,208			5,208		$ 12,434
Goodwill, Impairment Loss			$ 7,200
Goodwill, Impaired, Accumulated Impairment Loss		$ 7,200			7,200
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					$ 1,500

[1] The September 30, 2016 medical professional liability goodwill balance reflects a $7.2 million non-cash impairment charge recorded in the second quarter of 2016.