Earnings Per Common Share and Summary of Share-Based Award Transactions (Details) - SARs - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, SARS, Outstanding [Roll Forward]
Number Of Shares, Outstanding Beginning Balance	30	28
Number Of Shares, SARs granted	14	4
Number Of Shares, SARs exercised	(8)	(2)
Number Of Shares, Outstanding Ending Balance	36	30	28
Number Of Shares, Exercisable as of December 31, 2020	27
Number Of Shares, Unvested as of December 31, 2020	9
Share-based Compensation Arrangement by Share-based Payment Award, SARS, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 124.13	$ 110.27
Weighted Average Exercise Price, SARs granted	137.40	162.81
Weighted Average Exercise Price, SARs exercised	75.75	50.50
Weighted Average Exercise Price, Outstanding Ending Balance	139.16	$ 124.13	$ 110.27
Weighted Average Exercise Price, Exercisable as of December 31, 2020	139.31
Weighted Average Exercise Price, Unvested as of December 31, 2020	$ 138.70
Average Remaining Contractual Term, Outstanding Beginning Balance	4 years 4 months 17 days	3 years 6 months 10 days	3 years 7 months 20 days
Average Remaining Contractual Term, Exercisable as of December 31, 2020	3 years 8 months 8 days
Average Remaining Contractual Term, Unvested as of December 31, 2020	6 years 5 months 8 days
Aggregate Intrinsic Value, Outstanding Beginning Balance	$ 1,352	$ 2,019
Aggregate Intrinsic Value, Outstanding Ending Balance	903	$ 1,352	$ 2,019
Aggregate Intrinsic Value, Exercisable as of December 31, 2020	772
Aggregate Intrinsic Value, Unvested as of December 31, 2020	$ 131