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
Compensation and Retirement Disclosure [Abstract]
Dollar cap liability reduction		10.00%	10.00%	10.00%	10.00%	10.00%
Liability reduction	$ 6,338	$ 28,596	$ 3,960	$ 3,580	$ 4,289	$ 4,598	$ 40,414
Amortization period	2 months	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

The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Plan Amendment
-URI http://asc.fasb.org/extlink&oid=49173939

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration