Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Income Taxes
Income tax expense	$ 635	$ 362	$ 1,230	$ 483
Effective tax rate (as a percent)	(1.50%)	(1.60%)	(1.60%)