ACCUMULATED OTHER COMPREHENSIVE INCOME / (LOSS) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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			32,864
Amounts reclassifies from accumulated other comprehensive income			(10,181)
Total other comprehensive income / (loss)	68,858	(29,092)	22,683	(15,714)
Balance at end of period	46,563		46,563
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			32,864
Amounts reclassifies from accumulated other comprehensive income			(10,430)
Total other comprehensive income / (loss)			22,434
Balance at end of period	53,151		53,151
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			249
Total other comprehensive income / (loss)			249
Balance at end of period	$ (6,588)		$ (6,588)