Investments in Affiliates Accounted for Using the Equity Method (Investment in Lending Tree) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 172,975		$ 177,030
Share of earnings (losses)	$ (3,296)	$ (2,492)
LendingTree
Schedule of Equity Method Investments [Line Items]
Percentage ownership	26.90%
Market value	$ 1,210,769
Carrying amount	171,116		174,002
Share of earnings (losses)	(2,100)	$ (2,500)
Other
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 1,859		$ 3,028