Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions		3 Months Ended	12 Months Ended
	Mar. 22, 2018	Mar. 22, 2018	Dec. 31, 2019 USD ($) business	Dec. 31, 2018	Jun. 30, 2018
Summary of Significant Accounting Policies [Line Items]
Maximum Term of Contract			1 year
Automotive [Member]
Summary of Significant Accounting Policies [Line Items]
Finance Lease, Right-of-Use Asset | $			$ 4.1
Finance Lease, Liability, Current | $			$ 4.1
Graham Healthcare Group [Member] | Graham Holdings Company [Member]
Summary of Significant Accounting Policies [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent					90.00%
Hoover Treated Wood Products [Member] | Graham Holdings Company [Member]
Summary of Significant Accounting Policies [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent			98.01%
CSI Pharmarcy [Member] | Graham Holdings Company [Member]
Summary of Significant Accounting Policies [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent			75.00%
2026 [Member] | GHC One [Member]
Summary of Significant Accounting Policies [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners			5.00%
Transferred over Time [Member]
Summary of Significant Accounting Policies [Line Items]
Percentage of Revenue			73.00%	80.00%
Kaplan International [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Number of business lines | business			1
Higher Education [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations		1	1
Number of Performance Obligations In Contract With Tuition Cap		2
Transition and Operations Support Agreement Initial Term	30 years
Television Broadcasting [Member] | Advertising Revenue [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment			60 days
Television Broadcasting [Member] | Retransmission Revenue [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment			60 days
Manufacturing [Member]
Summary of Significant Accounting Policies [Line Items]
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment			90 days
Number of business lines | business			4
Manufacturing [Member] | Transferred over Time [Member]
Summary of Significant Accounting Policies [Line Items]
Percentage of Revenue			28.00%	27.00%
Health Care [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment			60 days
Health Care [Member] | Other Healthcare Services [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
SocialCode [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment			100 days
Automotive [Member]
Summary of Significant Accounting Policies [Line Items]
Number of Performance Obligations			1
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Investment maturity length			3 months
Amortized Intangible Assets, Useful Life (in years)			10 years
Lessee, Operating Lease, Renewal or Termination Option Term			10 years
Maximum [Member] | CSI Pharmarcy [Member]
Summary of Significant Accounting Policies [Line Items]
Percentage of Shares Eligible to be Redeemed			50.00%
Maximum [Member] | Machinery and Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)			20 years
Maximum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)			50 years
Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Lessee, Operating Lease, Renewal or Termination Option Term			1 year
Minimum [Member] | Machinery and Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)			3 years
Minimum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)			20 years