Share-Based Payments - Schedule of weighted average assumptions for valuation of stock options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Stock option disclosures
Proceeds from exercises of stock options	$ 16,220	$ 54,351	$ 26,663
Stock Option Awards
Weighted average assumptions relating to the valuation of stock options
Expected life (in years)	5 years	5 years	5 years
Expected volatility (as a percent)	27.20%	30.90%	47.30%
Risk-free interest rate (as a percent)	1.50%	1.60%	1.30%
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Stock option disclosures
Weighted average fair value of the stock options issued (in dollars per share)	$ 6.32	$ 8.78	$ 11.08
Aggregate fair value of stock options	$ 16,500	$ 10,000	$ 19,500
Aggregate intrinsic value of options exercised	11,000	86,700	50,300
Proceeds from exercises of stock options	16,200	54,400	26,700
Tax benefit realized for the tax deductions of stock option exercises	3,700	$ 31,700	$ 18,300
Total unrecognized compensation costs related to unvested stock option awards	$ 8,500
Weighted average period for recognition of unvested awards	1 year 9 months 18 days

Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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