Investments Career Builder (Details) - CareerBuilder, LLC and Dose Media, LLC - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Revenues, net	$ 152,358	$ 169,403	$ 312,828	$ 339,422
Operating income	9,731	3,180	16,061	10,034
Net income	$ 100,833	$ 5,508	$ 98,657	$ 13,248