Capital Stock, Stock Awards, and Stock Options (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	May 04, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cost of shares repurchased by company		$ 193,160,000	$ 71,386,000	$ 55,683,000
Shares subject to award outstanding		29,649	27,218
Number of shares forfeited due to modification		1,079
Number of shares awarded		14,630
Exercised, Number of Shares		3,060
Number of shares granted		0
Stock options outstanding		175,045	178,105
Dividends declared per common share		$ 6.60	$ 6.32	$ 6.04
Vested, Number of Shares		11,120
Kaplan Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, Number of Shares		0	0	0
Number of shares granted		0	0	0
Stock options outstanding		0
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares excluded from earnings per share		105,000	105,000	104,000
Maximum [Member] | Kaplan Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		5 years
Minimum [Member] | Kaplan Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Education [Member] | Kaplan Stock Option and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (credit)		$ 1,000,000	$ 1,000,000	$ 1,300,000
Accrual balance related to stock based compensation		12,300,000
Stock compensation payouts		$ 0	$ 0	$ 0
Class B Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Right to elect Board of Directors percentage		30.00%
Shares repurchased by company		325,134	121,761	93,969
Cost of shares repurchased by company		$ 195,000,000	$ 71,400,000	$ 55,700,000
Number of shares authorized to be repurchased					500,000
Authorized shares remaining for repurchase		236,403
Market value of company's stock (in dollars per share)		$ 696.52
Class B Common Stock [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (credit)		$ 3,900,000	3,400,000	3,900,000
Total unrecognized compensation expense		$ 8,900,000
Years over which cost expected to be recognized		2 years 1 month 6 days
Share awards outstanding, restriction will lapse in 2025		13,429
Share awards outstanding, restriction will lapse in 2027		16,220
Class B Common Stock [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (credit)		$ 1,200,000	$ 1,200,000	$ 1,700,000
Total unrecognized compensation expense		$ 3,200,000
Years over which cost expected to be recognized		2 years 8 months 12 days
Options outstanding exercisable now		136,415
Options outstanding exercisable in 2024 (shares)		12,876
Options outstanding exercisable in 2025 (shares)		12,877
Options outstanding exercisable in 2026 (shares)		12,877
Intrinsic value of options outstanding		$ 19,200,000
Intrinsic value of options exercisable		8,700,000
Intrinsic value of options unvested		$ 10,400,000
Options unvested, shares		38,630	51,841
Options unvested, average exercise price (in dollars per share)		$ 426.86	$ 429.57
Options unvested, weighted average remaining contractual term, years		6 years 8 months 12 days	7 years 8 months 12 days
Exercised, Number of Shares		3,060	5,084	0
Intrinsic value of options exercised		$ 500,000	$ 1,200,000
Tax benefit from stock option exercises		100,000	300,000
Class B Common Stock [Member] | Executive Officer | Share-based Payment Arrangement [Member] | Price-Based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (credit)		$ 1,100,000	$ 1,300,000
Vested, Number of Shares		0
Number of contingently issuable shares			1,000
Class B Common Stock [Member] | Executive Officer | Share-Based Payment Arrangement, Employee | Price-Based | Monte Carlo
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award other than Options, Grants in Periods, Grante Date Fair Value			$ 3,500,000
Class B Common Stock [Member] | Subsequent Event [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares awarded	1,006
Class B Common Stock [Member] | Maximum [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		10 years
Class B Common Stock [Member] | Minimum [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		6 years
Class B Common Stock [Member] | 2012 Incentive Compensation Plan [Member] | Share-based Payment Arrangement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance		191,474
Shares subject to award outstanding		191,474
Class B Common Stock [Member] | 2022 Incentive Compensation Plan | Share-based Payment Arrangement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for stock awards granted under the plan		500,000
Shares reserved for issuance		484,704
Shares subject to award outstanding		14,220
Shares available for future awards		498,924
Class B Common Stock [Member] | 2022 Incentive Compensation Plan | Share-based Payment Arrangement [Member] | non-employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares awarded		731	345
Stock-based compensation expense (credit)		$ 400,000	$ 200,000
Vested, Number of Shares		731	345
Kaplan Restricted Stock [Member] | Senior Manager [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares subject to award outstanding		7,206
Kaplan Restricted Stock [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of company common stock (in dollars per share)	$ 1,700