Accumulated Other Comprehensive Income / (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Apr. 30, 2014	Apr. 30, 2013
Components of accumulated other comprehensive income / (loss)
Beginning Balance	$ 103,702	$ 102,271
Other comprehensive income / (loss) before reclassifications	8,130	(5,196)
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income / (loss)	8,130	(5,196)
Ending Balance	111,832	97,075
Currency Translation Adjustments
Components of accumulated other comprehensive income / (loss)
Beginning Balance	103,438	102,220
Other comprehensive income / (loss) before reclassifications	8,060	(5,197)
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income / (loss)	8,060	(5,197)
Ending Balance	111,498	97,023
Accumulated Net Unrealized Gain on Investments
Components of accumulated other comprehensive income / (loss)
Beginning Balance	263	51
Other comprehensive income / (loss) before reclassifications	70	1
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income / (loss)	70	1
Ending Balance	333	52
Accumulated Net Unrealized Income / (Loss) On Hedging Contracts
Components of accumulated other comprehensive income / (loss)
Beginning Balance	1
Amounts reclassified from accumulated other comprehensive income
Ending Balance	$ 1