Balance Sheet Components - Equity-method investments (Additional Information) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Softbank Corp.
Variable Interest Entity [Line Items]
Accounts receivable	$ 2.7	$ 2.4

For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant