ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Net realized investment gains (losses)	$ 783		$ 1,262
Income tax expense (benefit), current	(9,205)		(4,102)
Total reclassification adjustment	1,771		1,508
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)	2,182		1,630
Income tax expense (benefit), current	(764)		(571)
Total reclassification adjustment	1,418		1,059
Unrecognized pension and postretirement benefit obligations | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net actuarial loss	(284)	[1]	(136)	[1]
Prior service credit	827	[1]	827	[1]
Total before tax	543		691
Income tax expense (benefit), current	(190)		(242)
Total reclassification adjustment	$ 353		$ 449

[1] These reclassified accumulated other comprehensive income components are included in the computation of net periodic pension and postretirement benefit income (see Note 5, Employee Retirement Plans, for additional details).