Summary of Significant Accounting Policies Effect of adopting new accounting guidance (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 0		$ 0
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 280		$ 280
Other Postretirement Benefit Plans, Defined Benefit [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service cost reported in operating income	7	21	14	43
Defined Benefit Plan, Net Periodic Benefit Cost reported in non-operating income	78	$ 93	156	$ 187
Other Postretirement Benefit Plans, Defined Benefit [Member] | Operating Income (Loss) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service cost reported in operating income	7		14
Other Postretirement Benefit Plans, Defined Benefit [Member] | Other Nonoperating Income (Expense) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost reported in non-operating income	$ 71		$ 142