Employee Benefit Plans: Change in Accounting Principle (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Effect of Change on Net Income	$ 0.4
Decrease in Prior Service Costs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Effect of Adoption	0.6
increase in Income Tax Expense
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Effect of Adoption	$ 0.2

Amount of the effect of a change in accounting principle on net income.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration