Summary of Significant Accounting Policies - Summary of Changes in Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Accounting Policies [Abstract]
Deferred product revenue - current, beginning balance	$ 445	$ 149
Deferred product revenue - current, additions	662	634
Deferred product revenue - current, deductions	(468)	(313)
Deferred product revenue - current, ending balance	639	470
Deferred product revenue - non current, beginning balance	15	46
Deferred product revenue - non current, deductions	(8)	(8)
Deferred product revenue - non current, ending balance	$ 7	$ 38

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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