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Derivative Instruments - Effects of Trading Activities on Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Trading Activity, Gains and Losses, Net [Line Items] |  |  |
Unrealized gain (loss) on forward contracts Revenue | $ (352) | $ 18 | $ 116
Total | 2,356 | 2,256 | 1,824
Revenue [Member] | Forward Contracts [Member] |  |  |
Trading Activity, Gains and Losses, Net [Line Items] |  |  |
Unrealized gain (loss) on forward contracts Revenue | (339) | 41 | 284
Revenue [Member] | Forward Contracts [Member] | Put Option [Member] |  |  |
Trading Activity, Gains and Losses, Net [Line Items] |  |  |
Realized gain on forward contracts/put option Revenue | $ 2,695 | $ 2,215 | $ 1,540

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- Definition Realized gain on derivatives. + References No definition available. + Details
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- Definition Net Increase or Decrease in the fair value of the derivative or group of derivatives included in earnings. + References 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 + Details
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- Details
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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FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: 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=6943989&loc=d3e3602-108585 + Details
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