Employee and Retiree Benefits Postretirement Plan Amendments (Details) - USD ($) $ in Thousands	1 Months Ended						12 Months Ended
	Jan. 31, 2017	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%	10.00%
Liability reduction		$ 28,596	$ 3,960	$ 3,580	$ 4,289	$ 4,598	$ 40,414
Amortization period		6 years 10 months 24 days	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]
Liability reduction	$ 6,338
Amortization period	2 months