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Stock-Based Compensation and Directors Stock Purchase Plan (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining number of shares available for issuance under the plan	2,012,451
Stock-based compensation	$ 14.9	$ 13.9	$ 12.8
Total tax benefit recognized from compensation arrangements	3.0	3.0	3.2
Fair value of shares vested during the period	18.0	$ 19.9	$ 21.5
Unrecognized compensation cost related to unvested SAR's and stock awards	$ 28.1
Compensation cost is expected to be recognized over a weighted average period, years	2 years 10 months 24 days
Common stock dividend rate percentage	5.00%
Nonvested Stock Award [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	4 years
Nonvested Stock Award [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	7 years
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	4 years
Contractual terms of awards granted (in years)	10 years
Directors Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining number of shares available for issuance under the plan	13,470
Number of shares purchased under stock option plan	22,139	22,625
Average price of shares purchased under stock option plan	$ 60.53	$ 58.27

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