Income Taxes - U.S. and Foreign Components of Earnings Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components Of Earnings From Continuing Operations Before Income Taxes And Provision For Income Taxes [Line Items]
U.S.	$ 332,607	$ 313,429	$ 282,774
Foreign	(5,701)	(1,264)	1,854
Income before income tax expense	326,906	312,165	284,628
LAMAR MEDIA CORP. AND SUBSIDIARIES [Member]
Components Of Earnings From Continuing Operations Before Income Taxes And Provision For Income Taxes [Line Items]
U.S.	332,989	313,801	283,107
Foreign	(5,701)	(1,264)	1,854
Income before income tax expense	$ 327,288	$ 312,537	$ 284,961