Income Tax (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018 USD ($) percentagepoints	Oct. 31, 2017 USD ($)	Oct. 31, 2018 USD ($) percentagepoints	Oct. 31, 2017 USD ($)
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	35.00%
Effective tax rate, percent	8.60%	32.60%	15.60%	31.30%
Effective tax rate, excluding discrete items	18.70%		19.30%
Effective tax rate change, excluding discrete items | percentagepoints	14		11
Impact of TCJA, excluding discrete items	$ 1,971		$ 6,320
Net tax benefit from discrete items	1,440		2,129
Total Discrete tax benefit (expense), net	$ 1,440	$ (9)	$ 2,129	$ (521)