Debt - Interest Rate Swaps (Details) - Cash Flow Hedging - Designated as Hedging Instrument - Interest rate swap contracts - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2016	Sep. 30, 2016
Derivative [Line Items]
Pay fixed swaps - notional amount	$ 400,000	$ 403,125
Net unrealized gain (loss)	$ 3,334	$ (5,834)
Weighted-average maturity period (years)	3 years 7 months 6 days	3 years 10 months 25 days
Weighted-average received rate	0.77%	0.53%
Weighted-average pay rate	1.26%	1.26%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

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- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

+ References

No definition available.

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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