Investments and Fair Value Measurements Investments in Privately Held Companies (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Equity securities without readily determinable fair values	$ 5,887		$ 9,862
Debt Securities, Available-for-sale [Line Items]
Equity method investments	0
Equity method investments	0		$ 45,913
Impairment on equity investment	$ 3,975	$ 0