ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Net realized investment gains (losses)		$ (1,085)	$ 783
Income tax expense, current		(7,618)	(9,205)
Total reclassification adjustment		791	1,771
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)		829	2,182
Income tax expense, current		(290)	(764)
Total reclassification adjustment		539	1,418
Unrecognized pension and postretirement benefit obligations | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net actuarial loss	[1]	(429)	(284)
Prior service credit	[1]	817	827
Total before tax		388	543
Income tax expense, current		(136)	(190)
Total reclassification adjustment		$ 252	$ 353

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