DERIVATIVE FINANCIAL INSTRUMENTS (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Gain (Loss) on Derivatives in Cash Flow Hedging Relationship
Cash posted as collateral related to derivative transactions	$ 20,200,000		$ 20,200,000
Securities posted as collateral related to derivative transactions	55,000,000		55,000,000
Cash received as collateral related to derivative transactions	12,000,000		12,000,000
Cash flow hedges
Gain (Loss) on Derivatives in Cash Flow Hedging Relationship
Expected reclassification out of accumulated other comprehensive income (loss) into earnings during the next twelve months			3,600,000
Cash flow hedges | Interest rate
Gain (Loss) on Derivatives in Cash Flow Hedging Relationship
Gain (loss) recognized in other comprehensive income (effective portion)	(2,000)	(248,000)	(75,000)	(343,000)
Gain (loss) reclassified from accumulated other comprehensive income into income (effective portion)	(858,000)	(895,000)	(1,712,000)	(1,778,000)
Cash flow hedges | Inflation
Gain (Loss) on Derivatives in Cash Flow Hedging Relationship
Gain (loss) recognized in other comprehensive income (effective portion)	(7,939,000)	(5,907,000)	985,000	2,184,000
Gain (loss) reclassified from accumulated other comprehensive income into income (effective portion)	(113,000)	(250,000)	67,000	(1,328,000)
Gain (loss) recognized in income (ineffective portion)	$ (870,000)	$ (617,000)	$ (224,000)	$ 28,000