Operations and summary of significant accounting policies - Reconciliation Of Denominators Used To Calculate Basic And Diluted EPS (Details) - shares shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Weighted average shares outstanding - basic (in shares)	131,722	131,987	130,300
Plus: Common share equivalents, Stock options and RSUs (in shares)	1,012	1,287	1,087
Weighted average shares outstanding - diluted (in shares)	132,734	133,274	131,387

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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