ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 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	(36,975)
Amounts reclassifies from accumulated other comprehensive income	(9,200)
Total other comprehensive income / (loss)	(46,175)	13,378
Balance at end of period	(22,295)
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	(36,975)
Amounts reclassifies from accumulated other comprehensive income	(9,325)
Total other comprehensive income / (loss)	(46,300)
Balance at end of period	(15,583)
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	125
Total other comprehensive income / (loss)	125
Balance at end of period	$ (6,712)