SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets
Goodwill	$ 46,062,000	$ 49,657,000
State insurance licenses	7,500,000	7,500,000
Definite-lived intangibles, net of accumulated amortization of $3,062 at 12/31/18 and $5,678 at 12/31/17	972,000	2,145,000
Accumulated amortization of definite-lived intangibles	3,062,000	5,678,000
Total intangibles	8,472,000	9,645,000
Goodwill and intangibles	54,534,000	59,302,000
Goodwill and Intangible Asset Impairment	4,400,000
Amortization of intangible assets	400,000	700,000	$ 900,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	400,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	400,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	100,000
Energy Surety
Goodwill and Intangible Assets
Goodwill	25,706,000	25,706,000
Miscellaneous and Contract Surety
Goodwill and Intangible Assets
Goodwill	15,110,000	15,110,000
Small commercial
Goodwill and Intangible Assets
Goodwill	5,246,000	5,246,000
Medical professional liability
Goodwill and Intangible Assets
Goodwill	0	3,595,000
Casualty segment | Medical professional liability
Goodwill and Intangible Assets
Goodwill, Impaired, Accumulated Impairment Loss	12,400,000	8,800,000
Goodwill and Intangible Asset Impairment	4,400,000	3,400,000
Goodwill, Impairment Loss	3,600,000	1,600,000	$ 7,200,000
Impairment of Intangible Assets, Finite-lived	$ 800,000	$ 1,800,000