Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 16,930	$ 17,248
Depreciation and amortization	4,000	3,300	$ 2,900
Lease and loaner instruments
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 2,400	$ 1,900