Significant Accounting Policies - Revenue by Major Customers (Detail) - Revenues - Customer Concentration Risk	3 Months Ended	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Private
Concentration Risk [Line Items]
Concentration risk percentage	39.40%	30.70%	39.40%	31.40%
Public
Concentration Risk [Line Items]
Concentration risk percentage	60.60%	69.30%	60.60%	68.60%

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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