CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (PARENTHETICAL) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized (loss) / gain on investments, tax (benefit)	$ (13)	$ 30	$ (15)
Net change in effective portion of hedging contracts, tax (benefit)	(9)	$ (10)	$ 10
Tax effect of tax rate change on marketable securities	$ 21