Accumulated other comprehensive income/(loss) Reclassifications out of AOCI (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cash flows from derivative financial instruments related to interest payments made for the hedged debt instrument	$ 34,326	$ 30,862	$ 42,549
Total reclassifications for the period	(31,496)	(6,888)	(87,596)
Reclassification out of AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	3,581	6,129
Interest expense | Derivative financial instruments | Reclassification out of AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cash flows from derivative financial instruments related to interest payments made for the hedged debt instrument	$ 3,581	$ 6,129