Retirement plans Reconciliation of benefit obligations, plan assets and funded status (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan vested benefit obligation	$ 6,658	$ 6,500
Defined Benefit Plan, Accumulated Benefit Obligation	6,658	6,500
Defined Benefit Plan, Benefit Obligation	6,658	6,500	$ 7,020
Interest cost	253	278
Actuarial loss (gain)	249	(493)
Benefits paid	344	305
Fair value of plan assets	6,700	6,228	$ 5,883
Actual gain on plan assets	816	650
Unfunded status	42	(272)
Prepaid expenses and other current assets	349	348
Total other assets	7,757	7,512
Deferred compensation liabilities	(1,657)	(1,821)
Net amount recognized	42	(272)
OCI unrecognized actuarial loss	1,307	1,472
OCI net amount recognized	1,307	1,472
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total other assets	$ 1,350	$ 1,201