Summary of Significant Accounting Policies - Schedule of Revenue by Major Customers by Geographic Area (Detail)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Revenue [Member] \| Geographic Concentration Risk [Member] \| United States [Member]
Concentration Risk [Line Items]
Revenue	80.00%	81.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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