Share Based Compensation - Outstanding stock units (Details) - Director	12 Months Ended
	Jan. 31, 2019 $ / shares shares
Number of stock units
Outstanding, beginning of period (in shares) | shares	87,614
Granted (in shares) | shares	13,713
Deferred retainers (in shares) | shares	2,560
Dividends (in shares) | shares	1,338
Outstanding, end of period (in shares) | shares	105,225
Weighted average price
Outstanding, beginning of period (in usd per share) | $ / shares	$ 19.35
Granted (in usd per share) | $ / shares	39.25
Deferred retainers (in usd per share) | $ / shares	39.05
Dividends (in usd per share) | $ / shares	38.99
Outstanding, end of period (in usd per share) | $ / shares	$ 22.67