Summary of Significant Accounting Policies Effect of adopting new accounting guidance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 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
Reclass of Stranded Tax Effect in AOCI	$ 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	21	64
Defined Benefit Plan, Interest Cost and other reported in nonoperating income (expense)	79	$ 83	237	$ 247
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		21
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, Interest Cost and other reported in nonoperating income (expense)	$ 71		$ 213