ACCUMULATED OTHER COMPREHENSIVE INCOME - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2016	$ 46,081
Other comprehensive income before reclassifications	9,705
Amounts reclassified from accumulated other comprehensive income	(1,351)
Other comprehensive income (loss)	8,354	$ 11,484
Balance at March 31, 2017	54,435
Unrealized Gains and (Losses) on Available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2016	49,748
Other comprehensive income before reclassifications	9,705
Amounts reclassified from accumulated other comprehensive income	(1,079)
Other comprehensive income (loss)	8,626
Balance at March 31, 2017	58,374
Unrecognized pension and postretirement benefit obligations
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2016	(3,667)
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income	(272)
Other comprehensive income (loss)	(272)
Balance at March 31, 2017	$ (3,939)