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INTEREST RATE SWAP AGREEMENTS (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 item	Dec. 31, 2011 item
INTEREST RATE SWAP AGREEMENTS
Number of interest rate swap agreements outstanding	5	8
Interest rate swaps designated as cash flow hedges
Notional amount outstanding	$ 356,233	$ 606,233
Interest rate swap, with 4.485% fixed rate and start date of 14 September, 2005
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	4.485%	4.485%
Notional amount outstanding	106,233	106,233
Interest rate swap, with 5.25% fixed rate and start date of 2 January, 2007
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	5.25%	5.25%
Notional amount outstanding	50,000	50,000
Interest rate swap, with 5.075% fixed rate and start date of 2 January, 2008
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	5.075%	5.075%
Notional amount outstanding	50,000	50,000
Interest rate swap, with 5.07% fixed rate and start date of 2 January, 2008
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	5.07%	5.07%
Notional amount outstanding		100,000
Interest rate swap, with 4.985% fixed rate and start date of 31 March, 2008
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	4.985%	4.985%
Notional amount outstanding		50,000
Interest rate swap, with 5.04% fixed rate and start date of 31 March, 2008
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	5.04%	5.04%
Notional amount outstanding		100,000
Interest rate swap, with 2.05% fixed rate and start date of 22 January, 2009
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	2.05%	2.05%
Notional amount outstanding	100,000	100,000
Interest rate swap, with 2.45% fixed rate and start date of 23 February, 2009
Interest rate swaps designated as cash flow hedges
Fixed rate (as a percent)	2.45%	2.45%
Notional amount outstanding	$ 50,000	$ 50,000