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Investments - Summary of Investments by Type of Security (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 20,171	$ 34,075
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(86)	(16)
Fair Market Value	20,085	34,059
U.S. Treasury | Short-term investments
Schedule Of Available For Sale Securities [Line Items]
Cost	8,654	3,897
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(30)	(3)
Fair Market Value	8,624	3,894
Corporate debt securities | Short-term investments
Schedule Of Available For Sale Securities [Line Items]
Cost	10,572	26,393
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(50)	(8)
Fair Market Value	10,522	26,385
Corporate debt securities | Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Cost	945	3,785
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(5)
Fair Market Value	$ 939	$ 3,780

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

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-Publisher FASB
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