Employee and Retiree Benefits Postretirement Plan Amendments (Details) - USD ($) $ in Thousands	1 Months Ended					12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012	Aug. 27, 2005
Dollar cap liability reduction		10.00%	10.00%	10.00%	10.00%
Liability reduction		$ 3,960	$ 3,580	$ 4,289	$ 4,598	$ 40,414
Amortization period		7 years 1 month 6 days	7 years 4 months	7 years 6 months	7 years 9 months 20 days	11 years 6 months
Subsequent Event [Member]
Dollar cap liability reduction	10.00%
Liability reduction	$ 28,596
Amortization period	6 years 10 months 24 days