ACCUMULATED OTHER COMPREHENSIVE INCOME - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2014			$ 81,662
Other comprehensive income (loss) before reclassifications			(10,603)
Amounts reclassified from accumulated other comprehensive income			(5,526)
Other comprehensive income (loss)	$ (19,351)	$ 10,823	(16,129)	$ 20,209
Balance at June 30, 2015	65,533		65,533
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			(10,603)
Amounts reclassified from accumulated other comprehensive income			(4,875)
Other comprehensive income (loss)			(15,478)
Balance at June 30, 2015	62,884		62,884
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			(651)
Other comprehensive income (loss)			(651)
Balance at June 30, 2015	$ 2,649		$ 2,649