Amount of effect on financial statements related to corrections of prior period errors in the current period financial statements when the effect of the prior period error was immaterial to the prior period financial statements and the current period correction is immaterial to the current period financial statements.

No definition available.

Name:	ghc_ImmaterialErrorCorrectionAmount
Namespace Prefix:	ghc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Business Segments (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended
Business Segments (Narrative) (Details) $ in Millions	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2016 Segment
Business Segments [Line Items]
Number of reportable segments \| Segment			4
Education [Member]
Business Segments [Line Items]
Immaterial Error Correction Amount		$ 4.7
Periods from 2011 to Q2 2015 [Member] \| Test Preparation [Member] \| Reportable Subsegments [Member] \| Education [Member] \| Operating Segments [Member]
Business Segments [Line Items]
Immaterial Error Correction Amount	$ 3.0