Balance Sheet Components - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at the beginning of year	$ 204	$ 963	$ 1,063
Additions (deductions) charged (credited) to expense	17	(292)	335
Deductions/write-offs	(109)	(467)	(435)
Balance at the end of year	$ 112	$ 204	$ 963