Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable equity investments	$ 30,300,000	$ 36,100,000
Equity securities without readily determinable fair value, initial costs	44,100,000	36,100,000
Unrealized gain on equity investments remeasured at fair value	1,200,000
Cost-method investments impairment loss	15,000,000
Securities without readily determinable fair value, impairment losses		$ 0
Level III
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities without readily determinable fair value, initial costs	36,100,000
Equity Securities, FV-NI and without Readily Determinable Fair Value	$ 22,300,000