Hedging - Derivative Assets and Liabilities Table (Details) (Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2014		Mar. 31, 2014		Jun. 30, 2013		Mar. 31, 2013
Currency Hedge Portfolio
Change in Fair Value of Derivative Assets and Liabilities [Roll Forward]
Balance at beginning of year	$ (3,831)		$ (5,014)		$ (3,125)		$ (23,215)
Realized (gains) losses included in net income	1,414		1,229		4,766		5,601
Transfers			0				7,638	[1]
Purchases, net	0	[2]	277	[2]	62	[2]	541	[2]
Changes in fair value	1,906		(323)		(5,142)		6,310
Balance at end of year	(511)		(3,831)		(3,439)		(3,125)
Bunker Fuel Forward Contracts
Change in Fair Value of Derivative Assets and Liabilities [Roll Forward]
Balance at beginning of year	(634)		988		7,621		8,572
Realized (gains) losses included in net income	(61)		(175)		(2,151)		(2,839)
Transfers			0				0
Purchases, net	0	[2]	0	[2]	0	[2]	0	[2]
Changes in fair value	1,641		(1,447)		(7,673)		1,888
Balance at end of year	$ 946		$ (634)		$ (2,203)		$ 7,621

[1] Represents the fair value at the transfer date of positions where hedge accounting was terminated. See discussion above.

[2] 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