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Derivative Instruments - Effect of Cash Flow Hedges on Income Statement (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jul. 31, 2019
Jul. 31, 2018
Jul. 31, 2019
Jul. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]        
Total revenues $ 887,752 $ 671,720 $ 1,712,807 $ 1,290,363
Designated as Hedging Instrument | Revenues        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gains (losses) related to foreign currency forward contracts designated as cash flow hedges $ 896   $ 912