Investments in Affiliates Accounted for Using the Equity Method (Investment in Lending Tree) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 177,030	$ 114,655
Share of earnings (losses) of affiliates	$ 25,772	7,001	$ 11,831
LendingTree
Schedule of Equity Method Investments [Line Items]
Percentage ownership	26.60%
Market value	$ 756,197
Carrying amount	174,002	114,655
Share of earnings (losses) of affiliates	21,100	7,000	$ 11,800
Other
Schedule of Equity Method Investments [Line Items]
Carrying amount	$ 3,028	$ 0