ACCUMULATED OTHER COMPREHENSIVE INCOME - Components 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]
Balance at December 31, 2015	$ 58,433
Other comprehensive income before reclassifications	12,275
Amounts reclassified from accumulated other comprehensive income	(791)
Other comprehensive income (loss)	11,484	$ 3,222
Balance at March 31, 2016	69,917
Unrealized Gains and (Losses) on Available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2015	60,369
Other comprehensive income before reclassifications	12,275
Amounts reclassified from accumulated other comprehensive income	(539)
Other comprehensive income (loss)	11,736
Balance at March 31, 2016	72,105
Unrecognized pension and postretirement benefit obligations
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2015	(1,936)
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income	(252)
Other comprehensive income (loss)	(252)
Balance at March 31, 2016	$ (2,188)