Segment Information - Property and Equipment Net on Geographical Basis (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Property and equipment, net	$ 53,027	$ 48,837
United States
Segment Reporting Information [Line Items]
Property and equipment, net	38,058	39,593
United Kingdom
Segment Reporting Information [Line Items]
Property and equipment, net	7,801	4,296
Other countries
Segment Reporting Information [Line Items]
Property and equipment, net	$ 7,168	$ 4,948
Geographic Concentration Risk \| Property Plant and Equipment
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	100.00%	100.00%
Geographic Concentration Risk \| United States \| Property Plant and Equipment
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	72.00%	81.00%
Geographic Concentration Risk \| United Kingdom \| Property Plant and Equipment
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	15.00%	9.00%
Geographic Concentration Risk \| Other countries \| Property Plant and Equipment
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	13.00%	10.00%

Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(14))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(8))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(13))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PropertyPlantAndEquipmentNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant