Hedging - Derivative Assets and Liabilities Table (Details) (Derivatives designated as hedging instruments, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Currency Hedge Portfolio
Change in Fair Value of Derivative Assets and Liabilities [Roll Forward]
Balance at beginning of year	$ (5,014)		$ (23,215)
Realized (gains) losses included in net income	1,229		8,722
Transfers			7,638
Purchases, net	277	[1]	541	[1]
Changes in fair value	(323)		3,189
Balance at end of year	(3,831)		(3,125)
Bunker Fuel Forward Contracts
Change in Fair Value of Derivative Assets and Liabilities [Roll Forward]
Balance at beginning of year	988		8,572
Realized (gains) losses included in net income	(175)		(2,839)
Purchases, net	0	[1]	0	[1]
Changes in fair value	(1,447)		1,888
Balance at end of year	$ (634)		$ 7,621

[1] Purchases (sales) represent the cash premiums paid upon the purchase of euro put options or received upon the sale of euro call options. Bunker fuel and currency forward contracts require no up-front cash payment and have an initial fair value of zero; settlements on the forward contracts (swaps) occur upon their maturity