Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Apr. 30, 2017	Apr. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		$ 473,993
Other comprehensive income / (loss) before reclassifications		(1,810)	$ 17,792
Amounts reclassified from accumulated other comprehensive income	[1]	(77)	(126)
Net current-period other comprehensive income / (loss)		(1,887)	17,666
Ending Balance		464,520	458,786
Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		76,569	68,265
Other comprehensive income / (loss) before reclassifications		(1,730)	17,892
Net current-period other comprehensive income / (loss)		(1,730)	17,892
Ending Balance		74,839	86,157
Available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		197	189
Other comprehensive income / (loss) before reclassifications		(12)	6
Net current-period other comprehensive income / (loss)		(12)	6
Ending Balance		185	195
Hedging Contracts
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		14	51
Other comprehensive income / (loss) before reclassifications		(68)	(106)
Amounts reclassified from accumulated other comprehensive income	[1]	(77)	(126)
Net current-period other comprehensive income / (loss)		(145)	(232)
Ending Balance		(131)	(181)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		76,780	68,505
Ending Balance		$ 74,893	$ 86,171

[1] Amounts reclassified to earnings in the Consolidated Statements of Operations.