Business combinations and disposals (Schedule of the Valuation of the Intangible Assets Acquired) (Details) - USD ($) $ in Thousands		9 Months Ended
	Dec. 15, 2015	Jun. 30, 2016
Ascend Management Innovations LLC
Business Acquisition [Line Items]
Finite-lived intangible assets acquired		$ 22,300
Customer relationships | Assessments Australia
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life	6 years
Customer relationships | Ascend Management Innovations LLC
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life		19 years
Finite-lived intangible assets acquired		$ 20,400
Trade Names | Ascend Management Innovations LLC
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life		1 year
Finite-lived intangible assets acquired		$ 1,700
Technology-Based Intangible Assets | Ascend Management Innovations LLC
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life		8 years
Finite-lived intangible assets acquired		$ 200