Net Income per Common Share - Reconciliation between basic and diluted net income per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Net Income per Common Share
Net income (in dollars)	$ (39,295)	$ 12,043
Basic net income per share:
Basic common shares	48,025	48,781
Basic net income per share (in dollars per share)	$ (0.82)	$ 0.25
Diluted net income per share:
Basic common shares	48,025	48,781
Diluted restricted stock awards and stock options		993
Diluted common shares	48,025	49,774
Diluted net income per share (in dollars per share)	$ (0.82)	$ 0.24