Hedging Deferred net gains (losses) in AOCI expected to be reclassed into income (Details) (USD $) In Thousands, unless otherwise specified	6 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	$ (412)	$ 0	$ 0	$ (2,912)	$ (3,324)
Bunker fuel forward contracts [Member]
Derivative [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	4,017	(800)	(3,736)	3,072	2,553
Total [Member]
Derivative [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	$ 3,605	$ (800)	$ (3,736)	$ 160	$ (771)