Incentive Plans Including Share-Based Compensation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Instruments Other than Options Activity [Roll Forward]
Balance at January 1 (in shares)	939
Granted (in shares)	483	500	503
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	(116)
Vested (in shares)	(464)	(475)	(467)
Dividend equivalents (in shares)	38
Balance at December 31 (in shares)	880	939
Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]
Balance at January 1, weighted average grant date fair value (in dollars per share)	$ 44.30
Granted, weighted average grant date fair value (in dollars per share)	49.67	$ 47.60	$ 41.02
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value (in dollars per share)	$ 50.19
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 29,432	$ 23,393	$ 22,459
Vested, weighted average grant date fair value (in dollars per share)	$ 41.09
Dividend equivalents, weighted average grant date fair value (in dollars per share)	45.22
Balance at December 31, weighted average grant date fair value (in dollars per share)	$ 48.20	$ 44.30
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Award Vesting Period (in years)	3 years
Restricted Stock [Member]
Equity Instruments Other than Options Activity [Roll Forward]
Balance at January 1 (in shares)	36
Granted (in shares)	13	18	15
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	0
Vested (in shares)	(19)
Dividend equivalents (in shares)	1
Balance at December 31 (in shares)	31	36
Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]
Balance at January 1, weighted average grant date fair value (in dollars per share)	$ 44.29
Granted, weighted average grant date fair value (in dollars per share)	53.46	$ 44.68	$ 42.00
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value (in dollars per share)	0
Vested, weighted average grant date fair value (in dollars per share)	41.60
Dividend equivalents, weighted average grant date fair value (in dollars per share)	57.09
Balance at December 31, weighted average grant date fair value (in dollars per share)	$ 50.15	$ 44.29
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Award Vesting Period (in years)	3 years
Service-based awards [Member]
Equity Instruments Other than Options Activity [Roll Forward]
Granted (in shares)	300	300	300

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The weighted average fair value as of grant dates pertaining to a share-based award plan other than a stock option plan for dividend equivalents on shares outstanding during the period in accordance with the terms of the arrangement.

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The number of shares issuable under a share-based award plan pertaining to dividend equivalents on shares outstanding during the period on other than stock option plans.

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