Derivative Contracts (Details 2) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (10,515)	$ (23,549)
Forward Contracts [Member]
Derivative [Line Items]
Contract value	2,435		1,537
Fair value	2,436		1,585
Derivative, Gain (Loss) on Derivative, Net	1	(21)	49
Forward Contracts [Member] | 0 to 30 [Member]
Derivative [Line Items]
Contract value	285		472
Fair value	294		489
Derivative, Gain (Loss) on Derivative, Net	9		17
Contract days until maturity, lower range	0 days		0 days
Contract days until maturity, higher range	30 days		30 days
Forward Contracts [Member] | 31 to 60 [Member]
Derivative [Line Items]
Contract value	952		562
Fair value	957		579
Derivative, Gain (Loss) on Derivative, Net	5		18
Contract days until maturity, lower range	31 days		31 days
Contract days until maturity, higher range	60 days		60 days
Forward Contracts [Member] | 61 to 90 [Member]
Derivative [Line Items]
Contract value	121		503
Fair value	120		517
Derivative, Gain (Loss) on Derivative, Net	(1)		14
Contract days until maturity, lower range	61 days		61 days
Contract days until maturity, higher range	90 days		90 days
Forward Contracts [Member] | 91 to 120 [Member]
Derivative [Line Items]
Contract value	921		0
Fair value	911		0
Derivative, Gain (Loss) on Derivative, Net	(10)		0
Contract days until maturity, lower range	91 days		91 days
Contract days until maturity, higher range	120 days		120 days
Forward Contracts [Member] | 121 to 180 [Member]
Derivative [Line Items]
Contract value	156		0
Fair value	154		0
Derivative, Gain (Loss) on Derivative, Net	(2)		0
Contract days until maturity, lower range	121 days		121 days
Contract days until maturity, higher range	180 days		180 days
Forward Contracts [Member] | More than 180 [Member]
Derivative [Line Items]
Contract value			0
Fair value
Derivative, Gain (Loss) on Derivative, Net			$ 0
Contract days until maturity, higher range	180 days		180 days