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ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts reclassified out of each component of accumulated other comprehensive income
Investment securities gain (loss)			$ 240us-gaap_GainLossOnSaleOfSecuritiesNet		$ 482us-gaap_GainLossOnSaleOfSecuritiesNet				$ 240us-gaap_GainLossOnSaleOfSecuritiesNet	$ 482us-gaap_GainLossOnSaleOfSecuritiesNet	$ 789us-gaap_GainLossOnSaleOfSecuritiesNet
Interest income	37,741	37,139	37,536	37,393	37,133	35,558	34,992	32,595	149,809	140,278	128,445
Net actuarial losses									(1,070)	(2,461)	(2,381)
Net transition obligation									(17)	(17)	(17)
Prior service cost									(18)	(18)	(17)
Tax (expense) benefit									(20,389)us-gaap_IncomeTaxExpenseBenefit	112,247us-gaap_IncomeTaxExpenseBenefit
Net income (loss)	13,265us-gaap_NetIncomeLoss	8,230us-gaap_NetIncomeLoss	9,150us-gaap_NetIncomeLoss	9,808us-gaap_NetIncomeLoss	10,295us-gaap_NetIncomeLoss	10,204us-gaap_NetIncomeLoss	14,267us-gaap_NetIncomeLoss	137,309us-gaap_NetIncomeLoss	40,453us-gaap_NetIncomeLoss	172,075us-gaap_NetIncomeLoss	47,421us-gaap_NetIncomeLoss
Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Net income (loss)									(1,295)	(8,734)	(3,312)
Investment Securities \| Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Investment securities gain (loss)									(1,071)	6,266	(1,382)
Tax (expense) benefit									426	(2,511)
Net of tax									(645)	3,755	(1,382)
Derivatives \| Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Interest income										(394)	434
Tax (expense) benefit										(10,599)
Net of tax										(10,993)	434
Defined Benefit Plans \| Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Net actuarial losses									(1,070)	(2,461)	(2,381)
Net transition obligation									(17)	(17)	(17)
Prior service cost									(18)	(18)	(17)
Reclassification from Accumulated Other Comprehensive Income									(1,105)	(2,496)	(2,415)
Tax (expense) benefit									455	1,000	51
Net of tax									$ (650)	$ (1,496)	$ (2,364)