Investments in Affiliates Accounted for Using the Equity Method (Investment in Lending Tree) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 112,975		$ 114,655
Share of earnings (loss)	$ (2,492)	$ 1,723
LendingTree
Schedule of Equity Method Investments [Line Items]
Percentage ownership	27.00%
Market value	$ 1,057,952
Carrying amount	112,174		114,655
Share of earnings (loss)	(2,500)	$ 1,700
Other
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 801		$ 0