Investments - Summary of Investments by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 28,331	$ 26,810
Gross Unrealized Gains	1	11
Gross Unrealized Losses	(18)	(6)
Fair Market Value	28,314	26,815
U.S. Treasury [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost	12,904	12,907
Gross Unrealized Gains	1	8
Gross Unrealized Losses	(2)
Fair Market Value	12,903	12,915
Corporate debt securities [Member] \| Short-term [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost	15,427	11,949
Gross Unrealized Gains		2
Gross Unrealized Losses	(16)	(3)
Fair Market Value	$ 15,411	11,948
Corporate debt securities [Member] \| Long-term [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost		1,954
Gross Unrealized Gains		1
Gross Unrealized Losses		(3)
Fair Market Value		$ 1,952

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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