Accumulated Other Comprehensive Loss (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains/(losses) on cash flow hedges, Current period change excluding amounts reclassified from accumulated other comprehensive loss	$ (8,302)	$ (6,843)
Unrealized gains/(losses) on cash flow hedges, Amounts reclassified from accumulated other comprehensive loss	4,726	5,065
Unrealized gains/(losses) on cash flow hedges, Total change in accumulated other comprehensive loss	(3,576)	(1,778)
Items not yet recognized as a component of net periodic benefit cost, Current period change excluding amounts reclassified from accumulated other comprehensive loss	496	(104)
Items not yet recognized as a component of net periodic benefit cost, Total change in accumulated other comprehensive loss	496	(104)
Current period change excluding amounts reclassified from accumulated other comprehensive loss	(7,806)	(6,947)
Amounts reclassified from accumulated other comprehensive loss	4,726	5,065
Total change in accumulated other comprehensive loss	(3,080)	(1,882)
Tax Expense Benefit [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains/(losses) on cash flow hedges, Current period change excluding amounts reclassified from accumulated other comprehensive loss	316
Unrealized gains/(losses) on cash flow hedges, Amounts reclassified from accumulated other comprehensive loss	0
Unrealized gains/(losses) on cash flow hedges, Total change in accumulated other comprehensive loss	316
Items not yet recognized as a component of net periodic benefit cost, Current period change excluding amounts reclassified from accumulated other comprehensive loss	0
Items not yet recognized as a component of net periodic benefit cost, Amounts reclassified from accumulated other comprehensive loss	0
Items not yet recognized as a component of net periodic benefit cost, Total change in accumulated other comprehensive loss	0
Current period change excluding amounts reclassified from accumulated other comprehensive loss	316
Amounts reclassified from accumulated other comprehensive loss	0
Total change in accumulated other comprehensive loss	$ 316