ACCUMULATED OTHER COMPREHENSIVE INCOME - Components 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]
Balance at December 31, 2014	$ 81,662
Other comprehensive income before reclassifications	4,993
Amounts reclassified from accumulated other comprehensive income	(1,771)
Other comprehensive income (loss)	3,222	9,386
Balance at March 31, 2015	84,884
Unrealized Gains and (Losses) on Available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2014	78,362
Other comprehensive income before reclassifications	4,993
Amounts reclassified from accumulated other comprehensive income	(1,418)
Other comprehensive income (loss)	3,575
Balance at March 31, 2015	81,937
Unrecognized pension and postretirement benefit obligations
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2014	3,300
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income	(353)
Other comprehensive income (loss)	(353)
Balance at March 31, 2015	$ 2,947