Balance Sheet Information - Notes Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jul. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 3,849		$ 1,082
Current portion of notes receivable	3,849		0
Reserve against current portion of notes receivable	(3,355)		0
Current portion of notes receivable, net	494		0
Notes receivable, net of current portion	0		1,082
Yonder Media Mobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	3,355		506
Notes receivable, net of current portion		$ 3,355
ValidSoft Ltd
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 494		$ 576