ACCUMULATED OTHER COMPREHENSIVE INCOME - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2014			$ 81,662
Other comprehensive income (loss) before reclassifications			(14,855)
Amounts reclassified from accumulated other comprehensive income			(6,003)
Other comprehensive income (loss)	$ (4,729)	$ (990)	(20,858)	$ 19,219
Balance at September 30, 2015	60,804		60,804
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 (loss) before reclassifications			(14,855)
Amounts reclassified from accumulated other comprehensive income			(5,039)
Other comprehensive income (loss)			(19,894)
Balance at September 30, 2015	58,468		58,468
Unrecognized pension and postretirement benefit obligations
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2014			3,300
Other comprehensive income (loss) before reclassifications			0
Amounts reclassified from accumulated other comprehensive income			(964)
Other comprehensive income (loss)			(964)
Balance at September 30, 2015	$ 2,336		$ 2,336