Balance Sheet Components - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Parenthetical) (Details)

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Balance Sheet Components - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Parenthetical) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Rental equipment, allowance	$ 524	$ 594