Share Based Compensation - Outstanding stock units (Details) - Director	12 Months Ended
	Jan. 31, 2018 $ / shares shares
Number of stock units
Outstanding, beginning of period (in shares) | shares	98,649
Granted (in shares) | shares	12,000
Deferred retainers (in shares) | shares	1,143
Dividends (in shares) | shares	1,547
Vested (in shares) | shares	(25,725)
Outstanding, end of period (in shares) | shares	87,614
Weighted average price
Outstanding, beginning of period (in usd per share) | $ / shares	$ 20.82
Granted (in usd per share) | $ / shares	35.00
Deferred retainers (in usd per share) | $ / shares	35.00
Dividends (in usd per share) | $ / shares	33.98
Vested (in usd per share) | $ / shares	33.88
Outstanding, end of period (in usd per share) | $ / shares	$ 19.35