ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income Loss [Line Items]
Net realized investment gains		$ 6,153	$ 4,349	$ 8,997
Income tax expense, current		(18,611)	(7,280)	(16,927)
Total reclassification adjustment		6,243	6,451	4,426
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		7,624	7,195	8,997
Income tax expense, current		(2,668)	(2,518)	(3,149)
Total reclassification adjustment		4,956	4,677	5,848
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]	(1,327)	(578)	(2,895)
Prior service credit	[1]	3,307	3,307	708
Total before tax		1,980	2,729	(2,187)
Income tax expense, current		(693)	(955)	765
Total reclassification adjustment		$ 1,287	$ 1,774	$ (1,422)

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