Summary of Significant Accounting Policies Earnings Per Share (Details) - shares	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Basic (in shares)	44,379	44,371	44,354	44,323	44,226	44,216	44,203	44,179	44,357,000	44,206,000	44,153,000
Performance shares (in shares)									242,000	221,000	69,000
Restricted stock (in shares)									47,000	47,000	42,000
Weighted average diluted common and potential common shares outstanding (in shares)	44,634	44,716	44,815	44,734	44,401	44,591	44,493	44,463	44,646,000	44,474,000	44,264,000

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

+ References

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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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Number of shares of restricted stock determined by relating the portion of time within a reporting period that restricted shares have been outstanding to the total time in that period. Restricted shares are subject to sales, contractual, regulatory or other restrictions that prevent or inhibit the holder from freely disposing of them before the restriction ends.

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