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		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Net Income (Loss) per Common Share
Net income (loss)	$ (14,976)	$ 11,119	$ (54,271)	$ 23,162
Basic net income (loss) per share:
Basic common shares	48,214	48,450	48,121	48,619
Basic net income (loss) per share (in dollars per share)	$ (0.31)	$ 0.23	$ (1.13)	$ 0.48
Diluted net income (loss) per share:
Basic common shares	48,214	48,450	48,121	48,619
Diluted restricted stock awards and stock options		666		817
Diluted common shares	48,214	49,116	48,121	49,436
Diluted net income (loss) per share (in dollars per share)	$ (0.31)	$ 0.23	$ (1.13)	$ 0.47