OPERATING SEGMENT INFORMATION Major Products (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenue by major product
Net premiums earned	$ 183,595	$ 179,448	$ 540,739	$ 520,790
Casualty segment
Revenue by major product
Net premiums earned	115,619	105,160	336,572	305,842
Casualty segment | Commercial and personal umbrella
Revenue by major product
Net premiums earned	27,844	26,500	82,510	77,809
Casualty segment | General liability
Revenue by major product
Net premiums earned	20,821	20,146	61,573	60,725
Casualty segment | Commercial transportation
Revenue by major product
Net premiums earned	21,557	17,464	60,037	47,262
Casualty segment | Professional services
Revenue by major product
Net premiums earned	19,318	18,140	56,748	52,861
Casualty segment | P&C package business
Revenue by major product
Net premiums earned	11,706	10,257	33,973	29,815
Casualty segment | Executive products
Revenue by major product
Net premiums earned	4,716	4,459	14,126	13,745
Casualty segment | Medical professional liability
Revenue by major product
Net premiums earned	4,512	3,032	12,509	9,168
Casualty segment | Other casualty
Revenue by major product
Net premiums earned	5,145	5,162	15,096	14,457
Property segment
Revenue by major product
Net premiums earned	37,532	44,685	114,011	128,084
Property segment | Commercial property
Revenue by major product
Net premiums earned	16,819	18,546	51,528	57,498
Property segment | Marine
Revenue by major product
Net premiums earned	11,964	12,029	36,070	34,930
Property segment | Specialty Personal
Revenue by major product
Net premiums earned	6,186	6,535	18,731	19,982
Property segment | Property reinsurance
Revenue by major product
Net premiums earned	2,544	3,029	7,925	9,388
Property segment | Crop reinsurance
Revenue by major product
Net premiums earned	19	4,523		6,210
Net premiums earned			(243)
Property segment | Other property
Revenue by major product
Net premiums earned		23		76
Surety segment
Revenue by major product
Net premiums earned	30,444	29,603	90,156	86,864
Surety segment | Miscellaneous
Revenue by major product
Net premiums earned	11,714	10,659	34,304	31,316
Surety segment | Commercial surety product
Revenue by major product
Net premiums earned	7,221	7,546	22,030	22,039
Surety segment | Contract
Revenue by major product
Net premiums earned	6,906	7,472	20,332	21,091
Surety segment | Energy Surety
Revenue by major product
Net premiums earned	$ 4,603	$ 3,926	$ 13,490	$ 12,418