ACCUMULATED OTHER COMPREHENSIVE INCOME - Components of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2013				$ 59,010	[1]
Other comprehensive income (loss) before reclassifications				24,211	[1]
Amounts reclassified from accumulated other comprehensive income				(4,002)	[1]
Other comprehensive income (loss)	10,823		(23,729)	20,209	[1]	(18,245)
Balance at June 30, 2014	79,219	[1]		79,219	[1]
Unrealized Gains and (Losses) on Available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2013				48,376	[1]
Other comprehensive income (loss) before reclassifications				24,211	[1]
Amounts reclassified from accumulated other comprehensive income				(3,115)	[1]
Other comprehensive income (loss)				21,096	[1]
Balance at June 30, 2014	69,472	[1]		69,472	[1]
Unrecognized pension and postretirement benefit obligations
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2013				10,634	[1]
Other comprehensive income (loss) before reclassifications				0	[1]
Amounts reclassified from accumulated other comprehensive income				(887)	[1]
Other comprehensive income (loss)				(887)	[1]
Balance at June 30, 2014	$ 9,747	[1]		$ 9,747	[1]

[1] All amounts are net of tax. Amounts in parentheses indicate debits.