Share Based Compensation - Outstanding stock options (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2018 USD ($) $ / shares shares
Number of options
Outstanding, beginning of period (in shares) | shares	990,900
Granted (in shares) | shares	85,800
Exercised (in shares) | shares	(206,000)
Forfeited (in shares) | shares	(43,600)
Expired (in shares) | shares	(124,150)
Outstanding, end of period (in shares) | shares	702,950
Weighted average exercise price
Outstanding, beginning of period (in usd per share) | $ / shares	$ 24.58
Granted (in usd per share) | $ / shares	29.20
Exercised (in usd per share) | $ / shares	31.01
Forfeited (in usd per share) | $ / shares	19.05
Expired (in usd per share) | $ / shares	31.70
Outstanding, end of period (in usd per share) | $ / shares	$ 22.34
Aggregate intrinsic value, Outstanding, end of period | $	$ 11,396
Weighted average remaining contractual term (years), Outstanding, end of period	2 years 5 months 26 days
Number of options, outstanding exercisable, end of period | shares	331,717
Share-based compensation arrangement by share-based payment award, options, vested and expected to vest, outstanding, number | shares	702,950
Weighted average exercise price, Outstanding exercisable, end of period | $ / shares	$ 23.43
Share-based compensation arrangement by share-based payment award, options, vested and expected to vest, outstanding, weighted average exercise price | $ / shares	$ 22.34
Aggregate intrinsic value, Outstanding exercisable, end of period | $	$ 5,014
Weighted average remaining contractual term (years), Outstanding exercisable, end of period	1 year 11 months 12 days
Share-based compensation arrangement by share-based payment award, options, vested and expected to Vest, outstanding, weighted average remaining contractual term	2 years 5 months 26 days