ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Changes in accumulated other comprehensive income / (loss) by component, net of tax
Balance at beginning of period			$ 23,880
Other comprehensive income before reclassifications			31,417
Amounts reclassifies from accumulated other comprehensive income			(22,053)
Total other comprehensive income / (loss)	(13,319)	(61,576)	9,364	(77,289)
Balance at end of period	33,244		33,244
Accumulated Net Gains / (Losses) on Cash Flow Hedges
Changes in accumulated other comprehensive income / (loss) by component, net of tax
Balance at beginning of period			30,717
Other comprehensive income before reclassifications			31,417
Amounts reclassifies from accumulated other comprehensive income			(22,372)
Total other comprehensive income / (loss)			9,045
Balance at end of period	39,762		39,762
Accumulated Postretirement Benefits
Changes in accumulated other comprehensive income / (loss) by component, net of tax
Balance at beginning of period			(6,837)
Amounts reclassifies from accumulated other comprehensive income			319
Total other comprehensive income / (loss)			319
Balance at end of period	$ (6,518)		$ (6,518)