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 ($)	Feb. 28, 2018 business	Jan. 31, 2018 business	Apr. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) Restaurants	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) business	Dec. 31, 2019 USD ($) business Restaurants	Dec. 31, 2018 USD ($) business	Dec. 31, 2017 USD ($) business	Dec. 02, 2019 USD ($)	Dec. 01, 2019 USD ($)	Jul. 31, 2019 Restaurants	Jul. 11, 2019	Jan. 31, 2019 USD ($)	Aug. 31, 2018	Jul. 31, 2018	Jul. 12, 2018	May 31, 2018	Jun. 30, 2017	Feb. 28, 2017
Business Acquisition [Line Items]
Number of businesses acquired | business																			8	8	6
Cost of acquisition																			$ 211,800,000	$ 121,100,000	$ 318,900,000
Floor plan payable										$ 25,800,000									25,800,000
Pension and other post retirement benefits liabilities																		$ 59,100,000			59,100,000
Payments to Acquire Businesses, Net of Cash Acquired																			179,421,000	111,546,000	299,938,000
Acquisition-related costs										3,000,000.0				$ 1,500,000				4,100,000	3,000,000.0	1,500,000	4,100,000
Goodwill expected to be deductible for income tax purposes										70,700,000				32,300,000				$ 11,000,000.0	70,700,000	32,300,000	11,000,000.0
Revenues of acquired companies since acquisition date																			308,800,000
Operating loss of acquired companies since acquisition date																			5,000,000.0
Gain on Disposition of Business																			(564,000)	8,157,000	(569,000)
Interest expense										$ 7,192,000	$ 6,776,000	$ 8,386,000	$ 7,425,000	6,531,000	$ 6,135,000	$ 17,165,000	$ 8,071,000		29,779,000	37,902,000	33,886,000
Change in redemption value of redeemable noncontrolling interests																			$ 32,000	$ 413,000	$ (446,000)
Maximum [Member] | CSI Pharmarcy [Member]
Business Acquisition [Line Items]
Percentage of Shares Eligible to be Redeemed										50.00%									50.00%
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%
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%
Television Broadcasting [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																					2
Education [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																			1	5	2
Gain on Disposition of Business																				$ 8,200,000
Number Of Businesses Disposed | business																				3
Education [Member] | Professional (U.S.) [Member] | Professional Publications, Inc. [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																														100.00%
Education [Member] | Professional (U.S.) [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
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] | Genesis [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																																100.00%
Education [Member] | Kaplan International [Member] | Red Marker [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													1
Education [Member] | Test Preparation [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business								1
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
Gain on Disposition of Business														4,300,000			$ 4,300,000			$ 4,300,000
Gain Related to Contingent Consideration																			$ 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	1
Manufacturing [Member] | Hoover Treated Wood Products [Member]
Business Acquisition [Line Items]
Percentage of interest acquired									97.72%
Payments to Acquire Businesses, Net of Cash Acquired									$ 206,800,000
Fair value of redeemable noncontrolling interest acquired									$ 3,700,000
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	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] | Hometown Home Health and Hospice [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																															100.00%
Graham Healthcare Group [Member] | Graham Healthcare Group [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business					1
SocialCode [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																				1
SocialCode [Member] | Marketplace Strategy [Member]
Business Acquisition [Line Items]
Percentage of interest acquired																											100.00%
Other Businesses [Member]
Business Acquisition [Line Items]
Number of businesses acquired | business																			3
Number of Stores										3									3
Number of Restaurants | Restaurants										13									13
Other Businesses [Member] | Auto dealerships [Member]
Business Acquisition [Line Items]
Number of Stores																										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
Percentage of Shares Eligible to be Redeemed																										10.00%
Advance to Minority Shareholder																										$ 3,500,000
Interest Rate on Advance to Minority Shareholder																										6.00%
Other Businesses [Member] | Clyde's Restaurant Group [Member]
Business Acquisition [Line Items]
Number of Restaurants | Restaurants																								13
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%
Pinnacle Bank Term Loan [Member]
Business Acquisition [Line Items]
Loans Payable to Bank										$ 11,203,000				$ 0					$ 11,203,000	$ 0
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
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%