Balance Sheets Details - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance - beginning of period	$ (421)	$ (421)	$ (428)
Recoveries from bad debts	0	0	7
Write-offs and other	387	0	0
Allowance - end of period	$ (34)	$ (421)	$ (421)