Fair Value Measurements - Fair Value Measurement on Company's Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	$ 69,370	$ 131,316
Corporate Bonds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		47,531
Money Market Funds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	69,370	30,883
U.S. Government Treasuries [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		23,258
U.S. Agency Securities [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		16,033
Asset Backed Obligations [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		9,177
Supranational and Sovereign Debt [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		4,434
Recurring [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	69,370	131,316
Equity Investment	18,008
Derivative financial instruments, net	7,890	(27,842)
Other liabilities	(29,805)	(37,954)
Total	65,463	65,520
Recurring [Member] \| Corporate Bonds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		47,531
Recurring [Member] \| Money Market Funds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	69,370	30,883
Recurring [Member] \| U.S. Government Treasuries [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		23,258
Recurring [Member] \| U.S. Agency Securities [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		16,033
Recurring [Member] \| Asset Backed Obligations [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		9,177
Recurring [Member] \| Supranational and Sovereign Debt [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		4,434
Level 1 [Member] \| Recurring [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	69,370	54,141
Total	69,370	54,141
Level 1 [Member] \| Recurring [Member] \| Money Market Funds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments	69,370	30,883
Level 1 [Member] \| Recurring [Member] \| U.S. Government Treasuries [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		23,258
Level 2 [Member] \| Recurring [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		77,175
Derivative financial instruments, net	7,890	(27,842)
Total	7,890	49,333
Level 2 [Member] \| Recurring [Member] \| Corporate Bonds [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		47,531
Level 2 [Member] \| Recurring [Member] \| U.S. Agency Securities [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		16,033
Level 2 [Member] \| Recurring [Member] \| Asset Backed Obligations [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		9,177
Level 2 [Member] \| Recurring [Member] \| Supranational and Sovereign Debt [Member]
Available-for-sale securities:
Fair value, Measured on recurring basis, Investments		4,434
Level 3 [Member] \| Recurring [Member]
Available-for-sale securities:
Equity Investment	18,008
Other liabilities	(29,805)	(37,954)
Total	$ (11,797)	$ (37,954)

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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- Definition

Fair value of the entity's equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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- Definition

Fair value of asset after deduction of liability.

+ References

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- Definition

Fair value portion of other liabilities.

+ References

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