Changes in Accumulated Other Comprehensive Loss by Component, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance			$ 1,300,903
Other comprehensive income (loss) before reclassifications	$ (7,888)	$ 8,949	(15,937)	$ 10,735
Amounts reclassified from accumulated other comprehensive income (loss)		(23)	(13)	(9)
Total other comprehensive (loss) income	(7,888)	8,926	(15,950)	10,726
Ending Balance	1,443,672	1,308,813	1,443,672	1,308,813
Foreign Currency Translation
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(18,309)	(32,224)	(10,340)	(34,012)
Other comprehensive income (loss) before reclassifications	(7,881)	8,942	(15,850)	10,730
Total other comprehensive (loss) income	(7,881)	8,942	(15,850)	10,730
Ending Balance	(26,190)	(23,282)	(26,190)	(23,282)
Unrealized Gains and (Losses) on available- for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(404)	(45)	(311)	(57)
Other comprehensive income (loss) before reclassifications	(7)	7	(87)	5
Amounts reclassified from accumulated other comprehensive income (loss)		(23)	(13)	(9)
Total other comprehensive (loss) income	(7)	(16)	(100)	(4)
Ending Balance	(411)	(61)	(411)	(61)
Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(18,713)	(32,269)	(10,651)	(34,069)
Ending Balance	$ (26,601)	$ (23,343)	$ (26,601)	$ (23,343)

Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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