Interest rate hedge agreements Outstanding interest rate swap (Details) $ in Thousands	Sep. 30, 2017 USD ($) contract
Interest rate hedge agreements
Fair Values	$ 3,150
Notional Amount in Effect as of 9/30/17	1,008,000
Notional Amount in Effect as of 2017	1,026,000
Notional Amount in Effect as of 2018	750,000
Notional Amount in Effect as of 2019	$ 100,000
0.78% Interest rate swap, effective March 31, 2017
Interest rate hedge agreements
Number of Contracts \| contract	4
Interest Pay Rate (as a percent)	0.78%
Fair Values	$ 692
Notional Amount in Effect as of 9/30/17	250,000
Notional Amount in Effect as of 2017	250,000
Notional Amount in Effect as of 2018	0
Notional Amount in Effect as of 2019	$ 0
1.51% Interest rate swap, effective March 31, 2017
Interest rate hedge agreements
Number of Contracts \| contract	11
Interest Pay Rate (as a percent)	1.51%
Fair Values	$ (554)
Notional Amount in Effect as of 9/30/17	650,000
Notional Amount in Effect as of 2017	650,000
Notional Amount in Effect as of 2018	0
Notional Amount in Effect as of 2019	$ 0
2.00% Interest rate cap, effective July 29, 2016
Interest rate hedge agreements
Number of Contracts \| contract	2
Interest Pay Rate (as a percent)	2.00%
Fair Values	$ 66
Notional Amount in Effect as of 9/30/17	108,000
Notional Amount in Effect as of 2017	126,000
Notional Amount in Effect as of 2018	150,000
Notional Amount in Effect as of 2019	$ 0
1.16% Interest rate swap, effective March 29, 2018
Interest rate hedge agreements
Number of Contracts \| contract	8
Interest Pay Rate (as a percent)	1.16%
Fair Values	$ 2,975
Notional Amount in Effect as of 9/30/17	0
Notional Amount in Effect as of 2017	0
Notional Amount in Effect as of 2018	600,000
Notional Amount in Effect as of 2019	$ 0
1.89% Interest rate swap, effective March 29, 2019
Interest rate hedge agreements
Number of Contracts \| contract	1
Interest Pay Rate (as a percent)	1.89%
Fair Values	$ (29)
Notional Amount in Effect as of 9/30/17	0
Notional Amount in Effect as of 2017	0
Notional Amount in Effect as of 2018	0
Notional Amount in Effect as of 2019	$ 100,000

Effective Portion of Interest Rate Cash Flow Hedge at Fiscal Year End

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Effective Portion of Interest Rate Cash Flow Hedge in Year Three

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- Definition

Effective Portion of Interest Rate Cash Flow Hedge in Year Two

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- Definition

Effective Portion of Interest Rate Cash Flow Hedge in the Next Twelve Months

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- Definition

Average fixed interest rate that will be received or paid upon exercise of a group of interest rate swaption contracts.

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- Definition

Fair value as of the balance sheet date of all interest rate derivatives designated as cash flow hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

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