Acquisitions and Dispositions of Businesses (Narrative) (Details)		1 Months Ended							3 Months Ended									12 Months Ended
	Mar. 22, 2018 USD ($)	Nov. 30, 2019 business	Sep. 30, 2019 business	Mar. 31, 2019 USD ($)	Sep. 30, 2018 business	Jun. 30, 2018 USD ($)	Feb. 28, 2018 business	Jan. 31, 2018 business	Dec. 31, 2020 USD ($) automotiveDealership restaurant	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) business	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) business restaurant automotiveDealership	Dec. 31, 2019 USD ($) business	Dec. 31, 2018 USD ($) business	Jan. 26, 2021 USD ($)	May 31, 2020 USD ($)	Dec. 02, 2019 USD ($)	Dec. 01, 2019 USD ($)	Jul. 31, 2019 restaurant	Jul. 11, 2019	Jan. 31, 2019 USD ($) store	Aug. 31, 2018	Jul. 31, 2018	Jul. 12, 2018	May 31, 2018
Business Acquisition [Line Items]
Number of businesses acquired | business																		3	8	8
Cost of acquisition																		$ 96,800,000	$ 211,800,000	$ 121,100,000
Floor plan payable													$ 25,800,000						25,800,000
Payments to Acquire Businesses, Net of Cash Acquired																		20,080,000	179,421,000	111,546,000
Acquisition-related costs									$ 1,100,000				3,000,000.0					1,100,000	3,000,000.0	1,500,000
Goodwill expected to be deductible for income tax purposes									3,200,000				70,700,000					3,200,000	70,700,000	32,300,000
Revenues of acquired companies since acquisition date																		28,800,000
Operating loss of acquired companies since acquisition date																		(13,800,000)
Net gain (loss) on sale of businesses																		213,302,000	(564,000)	8,157,000
Interest expense									$ 16,008,000	$ 7,247,000	$ 7,377,000	$ 7,678,000	$ 7,192,000	$ 6,776,000	$ 8,386,000	$ 7,425,000		38,310,000	29,779,000	37,902,000
Change in redemption value of redeemable noncontrolling interests																		$ 273,000	$ 32,000	$ 413,000
Maximum [Member] | CSI Pharmarcy [Member]
Business Acquisition [Line Items]
Percentage of Shares Eligible to be Redeemed																								50.00%
Group of Senior Managers of GHG [Member] | GHC One [Member]
Business Acquisition [Line Items]
Percentage of Distributions Available to Common Unit Holders																		20.00%
Graham Holdings Company [Member] | GHC One [Member]
Business Acquisition [Line Items]
Guaranteed Return																		8.00%
Percentage of Distributions Available to Common Unit Holders																		80.00%
Education [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business												2						2	1	5
Net gain (loss) on sale of businesses																				$ 8,200,000
Number Of Businesses Disposed | business																				3
Education [Member] | Supplemental Education [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business								1				1
Number Of Businesses Disposed | business							1
Education [Member] | Supplemental Education [Member] | Professional Publications, Inc. [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																															100.00%
Education [Member] | Supplemental Education [Member] | College for Financial Planning [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																														100.00%
Education [Member] | Kaplan International [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business							1					1
Number Of Businesses Disposed | business		1
Education [Member] | Kaplan International [Member] | Heverald [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																										100.00%
Education [Member] | Kaplan International [Member] | Kaplan Australia [Member]
Business Acquisition [Line Items]
Number Of Businesses Disposed | business					1
Education [Member] | Higher Education [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Transition and Operations Support Agreement Initial Term	30 years
Transition and Operations Support Agreement Buy-Out Option Eligible Year	6 years
Transition and Operations Support Agreement Renewal Periods	5 years
Net gain (loss) on sale of businesses																	$ 4,300,000			$ 4,300,000
Gain Related to Contingent Consideration																		$ 3,500,000	$ 1,400,000	$ 1,900,000
First Five Years of Transition and Operations Support Agreement	5 years
Number of Consecutive Years of Purdue University Global Cash Operating Losses	3 years
Education [Member] | Higher Education [Member] | Minimum [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Annual Purdue University Global Cash Operating Losses	$ 25,000,000
Aggregate Purdue University Global Cash Operating Losses	$ 75,000,000
Education [Member] | Higher Education [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Percentage of Cost Efficiencies	20.00%
Education [Member] | Higher Education [Member] | Purdue University Global [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Percentage of Cost Efficiencies	20.00%
Advance Related To Kaplan University Transaction	$ 20,000,000
Education [Member] | Higher Education [Member] | After June 30, 2048 [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Kaplan University Transaction Termination Fee	75.00%
Purdue University Global Final Payment Note Duration	10 years
Education [Member] | Higher Education [Member] | After June 30, 2024 [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Kaplan University Transaction Termination Fee	125.00%
Purdue University Global Final Payment Note Duration	10 years
Education [Member] | Higher Education [Member] | After June 30, 2023 [Member] | Purdue University Global [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Percentage of Revenue Remaining To Be Paid	10.00%
Education [Member] | Higher Education [Member] | After June 30, 2027 [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Kaplan Share of Purdue University Global Revenue	12.50%
Education [Member] | Higher Education [Member] | July 1, 2022 through June 30, 2027 [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Kaplan Share of Purdue University Global Revenue	13.00%
Education [Member] | Higher Education [Member] | March 22, 2018 through June 30, 2022 [Member] | Kaplan [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Kaplan Share of Purdue University Global Revenue	12.50%
Education [Member] | Higher Education [Member] | March 22, 2018 through June 30, 2023 [Member] | Purdue University Global [Member] | Kaplan University Transaction [Member]
Business Acquisition [Line Items]
Amount of Priority Payment Per Year Beyond Costs	$ 10,000,000
Manufacturing [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																			1	1
Manufacturing [Member] | Hoover Treated Wood Products [Member]
Business Acquisition [Line Items]
Change in redemption value of redeemable noncontrolling interests				$ 600,000
Manufacturing [Member] | Joyce/Dayton Corp. [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business			1
Manufacturing [Member] | Group Dekko [Member] | Furnlite Inc [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																													100.00%
Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																			3	1
Percentage of interest acquired																									100.00%
Interest expense						$ 6,200,000
Graham Healthcare Group [Member] | CSI Pharmacy Holding Company, LLC [Member] [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																								75.00%
Redeemable Noncontrolling Interest																								$ 1,700,000
Graham Healthcare Group [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business					1
Other Businesses [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																		1	3	1
Number of Stores | automotiveDealership									3									3
Number of Restaurants | restaurant									11									11
Other Businesses [Member] | Auto dealerships [Member]
Business Acquisition [Line Items]
Number of Stores | store																											2
Amount Borrowed to Finance Business Acquisition																											$ 30,000,000
Derivative, Fixed Interest Rate																											4.70%
Percentage of interest acquired																											90.00%
Management Fee																			$ 2,300,000
Advance to Minority Shareholder																											$ 3,500,000
Interest Rate on Advance to Minority Shareholder																											6.00%
Percentage of Additional Ownership Available to be Acquired																											10.00%
Other Businesses [Member] | Clyde's Restaurant Group [Member]
Business Acquisition [Line Items]
Number of Restaurants | restaurant																									13
Other Businesses [Member] | Framebridge [Member]
Business Acquisition [Line Items]
Percentage of Shares Eligible to be Redeemed																						20.00%
Redeemable Noncontrolling Interest																						$ 6,000,000.0
Business Combination, Contingent Consideration, Liability																						$ 50,600,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage																						93.40%
Other Businesses [Member] | Code3 [Member] | Marketplace Strategy [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																												100.00%
Securities Subject to Mandatory Redemption [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Interest expense						$ 6,200,000												$ 8,500,000
Graham Holdings Company [Member] | CSI Pharmarcy [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent									75.00%									75.00%
Graham Holdings Company [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent				90.00%												90.00%
Graham Holdings Company [Member] | Manufacturing [Member] | Hoover Treated Wood Products [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent													98.01%						98.01%
GHC One [Member] | Group of Senior Managers of GHG [Member] | GHC One [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners									5.00%									5.00%
Pinnacle Bank Term Loan [Member]
Business Acquisition [Line Items]
Loans Payable to Bank									$ 10,692,000				$ 11,203,000					$ 10,692,000	$ 11,203,000
Pinnacle Bank Term Loan [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Loans Payable to Bank																							$ 11,250,000
Pinnacle Bank Term Loan [Member] | Graham Healthcare Group [Member] | CSI Pharmacy Holding Company, LLC [Member] [Member]
Business Acquisition [Line Items]
Loans Payable to Bank																							$ 11,250,000
Pinnacle Bank Term Loan [Member] | Subsequent Event [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Loans Payable to Bank																					$ 10,600,000
Group of Senior Managers of GHG [Member] | GHC One [Member]
Business Acquisition [Line Items]
Percentage of Contributed Capital																		5.00%
Graham Holdings Company [Member] | GHC One [Member]
Business Acquisition [Line Items]
Percentage of Contributed Capital																		95.00%