Investments (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investments [Abstract]
Equity method investments	$ 88,500		$ 90,900
Investments in marketable equity securities	1,500		1,200
Investments in non-marketable equity securities	61,800		$ 71,800
Write-down of non-marketable equity securities and note receivable	$ 17,741	$ 0