Income Taxes - Components of Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax assets:
Net operating loss carryforward	$ 2,405	$ 649
Deferred revenue	11,537	6,762
Deferred compensation	1,695	1,252
Inventory reserve	1,126	956
Non-qualified and non-employee stock option expense	4,410	3,393
Capitalized research and development	1,991	3,348
Research and development tax credit carryforward	2,722	2,386
Reserves, accruals, and other	1,239	1,067
Total deferred income tax assets	27,125	19,813
Deferred income tax liabilities:
Depreciation	(2,364)	(2,228)
Amortization	(1,473)	(1,979)
Other	(294)	(187)
Total deferred income tax liabilities	(4,131)	(4,394)
Net deferred income tax assets before valuation allowance	22,994	15,419
Valuation allowance	(3,479)	(1,700)
Net deferred income tax assets	$ 19,515	$ 13,719