Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 26,108	$ 17,732
Accrued professional fees	4,734	1,067
Accrued taxes	2,827	2,110
Accrued clinical and research expenses	1,279	1,545
Accrued interest	243	243
Accrued warranty	708	645	$ 394
Accrued other	3,491	2,686
Total accrued liabilities	$ 39,390	$ 26,028