Capital Stock, Stock Awards, and Stock Options (Earnings Per Share) (Details 5) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Earnings Per Share, Basic and Diluted, Including Two Class Method [Line Items]
Net income attributable to Graham Holdings Company common stockholders	$ 237,141	$ 77,615	$ 18,854	$ (33,245)	$ 145,881	$ 43,145	$ 57,081	$ 81,748	$ 300,365	$ 327,855	$ 271,206
Less: Dividends paid–common stock outstanding and unvested restricted shares									(29,970)	(29,553)	(28,617)
Undistributed earnings									$ 270,395	$ 298,302	$ 242,589
Percent allocated to common stockholders									99.45%	99.45%	99.39%
Undistributed earnings allocated to common stockholders									$ 268,917	$ 296,665	$ 241,115
Add: Dividends paid–common stock outstanding									29,812	29,387	28,423
Numerator for basic earnings per share									298,729	326,052	269,538
Add: Additional undistributed earnings due to dilutive stock options									4	13	10
Numerator for diluted earnings per share									$ 298,733	$ 326,065	$ 269,548
Weighted average shares outstanding (shares)	4,970	5,060	5,196	5,274	5,284	5,285	5,285	5,284	5,124	5,285	5,333
Denominator for diluted earnings per share (shares)									5,139	5,327	5,370
Graham Holdings Company Common Stockholders:
Basic net income per common share (in usd per share)	$ 47.45	$ 15.25	$ 3.61	$ (6.32)	$ 27.45	$ 8.12	$ 10.74	$ 15.38	$ 58.30	$ 61.70	$ 50.55
Earnings Per Share, Diluted (in usd per share)	$ 47.34	$ 15.22	$ 3.60	$ (6.32)	$ 27.25	$ 8.05	$ 10.65	$ 15.26	$ 58.13	$ 61.21	$ 50.20
Stock Option Plan [Member]
Schedule of Earnings Per Share, Basic and Diluted, Including Two Class Method [Line Items]
Add: Effect of dilutive stock options (shares)									15	42	37