Hedging Deferred net gains (losses) in AOCI expected to be reclassed into income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended			42 Months Ended
	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Foreign currency derivatives [Member]
Derivative [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	$ (2,479)	$ 0	$ 0	$ (13,672)	$ (16,151)
Bunker fuel forward contracts [Member]
Derivative [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	3,113	523	4	7,300	10,940
Total [Member]
Derivative [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	$ 634	$ 523	$ 4	$ (6,372)	$ (5,211)