Stock-Based Compensation (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) item $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Stock-based compensation
Total unrecognized compensation cost related to the unvested awards | $	$ 14.1
Total weighted average remaining term of unrecognized compensation costs	1 year 5 months 19 days
Compensation cost recognized | $	$ 19.5	$ 20.2	$ 18.4
Class A
Stock-based compensation
Shares available for future grants of new equity awards	829,213
Performance stock units
Stock-based compensation
Granted (in shares)	79,000	99,000	108,000
Total unrecognized compensation cost related to the unvested awards | $	$ 8.0
Total weighted average remaining term of unrecognized compensation costs	1 year 6 months 10 days
Compensation cost recognized | $	$ 7.5	$ 9.7	$ 9.8
Fair value assumptions
Weighted average grant-date fair value (in dollars per share) | $ / shares	$ 162.23	$ 106.37	$ 102.98
Performance stock units | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share) | $ / shares	$ 203.3
Second Amended and Restated 2004 Stock Incentive Plan
Stock-based compensation
Number of stock incentive plans | item	1
Second Amended and Restated 2004 Stock Incentive Plan | Employee Stock Option [Member]
Stock-based compensation
Outstanding (in shares)	0
Summary of stock option activity and related information
Outstanding at end of year (in shares)	0
Second Amended and Restated 2004 Stock Incentive Plan | Restricted Stock and Deferred Shares
Stock-based compensation
Vesting period	3 years
Percentage of stock options becoming exercisable	33.00%
Second Amended and Restated 2004 Stock Incentive Plan | Performance Shares and Deferred Shares
Stock-based compensation
Minimum service period	10 years
Minimum age	55 years
Second Amended and Restated 2004 Stock Incentive Plan | Performance stock units
Stock-based compensation
Vesting period	3 years
Period of time used to calculate the compound annual growth rate	3 years
Second Amended and Restated 2004 Stock Incentive Plan | Performance stock units | Minimum
Stock-based compensation
Percent of target shares a recipient may earn	0
Second Amended and Restated 2004 Stock Incentive Plan | Performance stock units | Maximum
Stock-based compensation
Percent of target shares a recipient may earn	2
Management Stock Purchase Plan | Maximum
Stock-based compensation
Percentage of annual incentive bonus that may be used to purchase RSU's	50.00%
Management Stock Purchase Plan | Class A
Stock-based compensation
Purchase price as percentage of fair market value of common stock on grant date	80.00%
Shares authorized	2,000,000
Shares available for future grants of new equity awards	680,944
Management Stock Purchase Plan | Restricted stock | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share) | $ / shares	$ 203.3
Management Stock Purchase Plan | Restricted stock units (RSUs)
Stock-based compensation
Minimum deferral period	3 years
Granted (in shares)	20,000	26,000	29,000
Total unrecognized compensation cost related to the unvested awards | $	$ 1.7
Total weighted average remaining term of unrecognized compensation costs	1 year 4 months 24 days
Compensation cost recognized | $	$ 1.3	$ 1.2	$ 0.9
Fair value assumptions
Expected life (years)	3 years	3 years
Expected stock price volatility (as a percent)	28.90%	33.70%
Expected dividend yield (as a percent)	0.80%	0.80%
Risk-free interest rate (as a percent)	4.50%	4.10%
Weighted average grant-date fair value (in dollars per share) | $ / shares	$ 68.94	$ 57.5	$ 47.26
Management Stock Purchase Plan | Restricted stock units (RSUs) | Minimum
Stock-based compensation
Vesting period	3 years