Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 125,070	$ 24,844	$ 214,670	$ 87,929
Foreign currency translation adjustments:
Translation adjustments arising during the period	(2,844)	11,470	(22,447)	34,776
Unrealized gains on available-for-sale securities:
Unrealized gains for the period, net	0	47,836	0	71,370
Pension and other postretirement plans:
Amortization of net prior service cost included in net income	69	118	215	358
Amortization of net actuarial gain included in net income	(3,295)	(1,567)	(7,956)	(4,958)
Total pension and other postretirement plans, before tax	(3,226)	(1,449)	(7,741)	(4,600)
Cash flow hedge (loss) gain	(6)	(72)	601	(215)
Other Comprehensive (Loss) Income, Before Tax	(6,076)	57,785	(29,587)	101,331
Income tax benefit (expense) related to items of other comprehensive (loss) income	874	(18,540)	1,976	(26,665)
Other Comprehensive (Loss) Income, Net of Tax	(5,202)	39,245	(27,611)	74,666
Comprehensive Income	119,868	64,089	187,059	162,595
Comprehensive income attributable to noncontrolling interests	(6)	(60)	(149)	(63)
Total Comprehensive Income Attributable to Graham Holdings Company	$ 119,862	$ 64,029	$ 186,910	$ 162,532