ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]
Net realized investment gains (losses)	$ 4,349		$ 8,997		$ 8,017
Income tax expense (benefit), current	(7,280)		(16,927)		(11,594)
Total reclassification adjustment	6,451	[1]	4,426	[1]
Unrealized Gains and (Losses) on Available-for-sale securities | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net realized investment gains (losses)	7,195	[1]	8,997	[1]
Income tax expense (benefit), current	(2,518)	[1]	(3,149)	[1]
Total reclassification adjustment	4,677	[1]	5,848	[1]
Unrecognized pension and postretirement benefit obligations | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net actuarial loss	(578)	[1],[2]	(2,895)	[1],[2]
Prior service credit	3,307	[1],[2]	708	[1],[2]
Total before tax	2,729	[1]	(2,187)	[1]
Income tax expense (benefit), current	(955)	[1]	765	[1]
Total reclassification adjustment	$ 1,774	[1]	$ (1,422)	[1]

[1] Amounts in parentheses indicate debits to net income

[2] These accumulated other comprehensive income components are included in the computation of net periodic pension and postretirement benefit cost (income) (see Note 12, Employee Retirement Plans, for additional details).