Derivative Instruments - Effects of Trading Activities on Condensed Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized gain (loss) on forward contracts Revenue	$ 49	$ 186
Total	1,178	288
Revenue [Member] \| Forward Contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized gain (loss) on forward contracts Revenue	(68)	214
Revenue [Member] \| Forward Contracts [Member] \| Options [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Gain (Loss) on Sale of Derivatives	$ 1,246	$ 74

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a),(c),(d),(e)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

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- Definition

Amount of increase in the fair value of derivatives recognized in the income statement.

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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