Employee Retirement Benefits - Pre-tax adjustment to accumulated benefit obligation (Details) (Other Postretirement Benefit Plan, Defined Benefit [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	$ 6,309	$ 2,918	$ 3,441
Total pre-tax accumulated other comprehensive loss	6,309	2,918	3,441
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	2,918	3,441	3,241
Recognized net (loss)	(152)	(183)	(210)
Amortization of transition obligation	0	0	(23)
Net actuarial (gain) loss	3,543	(340)	433
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 6,309	$ 2,918	$ 3,441