This amount represents the notional amount in effect at period end.

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The percentage of effective notional amount of interest rate hedge agreements.

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Fixed interest rate related to the interest rate derivative.

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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.

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- Definition

The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
-Subparagraph b(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959

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The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
-Subparagraph b(2)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80748-113994

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 17
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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- Definition

Aggregate notional amount of all interest rate derivatives designated as hedging instruments in cash flow hedges. Notional amount refers to the monetary amount specified in the interest rate derivative contract.

+ References

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=6935481&loc=SL5580258-113959

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6519104

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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=6935481&loc=SL5579245-113959

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Interest rate hedge agreements (Details) (USD $)	3 Months Ended		6 Months Ended
Interest rate hedge agreements (Details) (USD $)	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Interest rate hedge agreements
The percentage of effectiveness of interest rate hedge agreements (as a percent)	100.00%	100.00%	100.00%	100.00%
Interest rate cash flow hedge gain (loss) reclassified to interest expense	$ 5,300,000	$ 7,800,000	$ 10,700,000	$ 15,900,000
Interest rate cash flow hedge gain (loss) expected to be reclassified to interest expense in next fiscal year	20,800,000		20,800,000
Interest rate hedge agreements
Effective	450,000,000		450,000,000
Fair Value	(39,221,000)		(39,221,000)		(44,645,000)
Transaction Date December 2006, Interest Pay Rate 4.990%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	4.99%		4.99%
Notional Amount	50,000,000		50,000,000
Effective	50,000,000		50,000,000
Fair Value	(5,551,000)		(5,551,000)
Transaction Date October 2007, Interest Pay Rate 4.546%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	4.546%		4.546%
Notional Amount	50,000,000		50,000,000
Effective	50,000,000		50,000,000
Fair Value	(2,631,000)		(2,631,000)
Transaction Date October 2007, Interest Pay Rate 4.642%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	4.642%		4.642%
Notional Amount	50,000,000		50,000,000
Effective	50,000,000		50,000,000
Fair Value	(4,424,000)		(4,424,000)
Transaction Date October 2007, Interest Pay Rate 4.622%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	4.622%		4.622%
Notional Amount	25,000,000		25,000,000
Effective	25,000,000		25,000,000
Fair Value	(1,799,000)		(1,799,000)
Transaction Date October 2007, Interest Rate 4.625%.
Interest rate hedge agreements
Interest Pay Rate (as a percent)	4.625%		4.625%
Notional Amount	25,000,000		25,000,000
Effective	25,000,000		25,000,000
Fair Value	(1,801,000)		(1,801,000)
Transaction Date December 2006, Interest Pay Rate 5.015%.
Interest rate hedge agreements
Interest Pay Rate (as a percent)	5.015%		5.015%
Notional Amount	75,000,000		75,000,000
Effective	75,000,000		75,000,000
Fair Value	(8,378,000)		(8,378,000)
Transaction Date December 2006, Interest Pay Rate 5.023%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	5.023%		5.023%
Notional Amount	75,000,000		75,000,000
Effective	75,000,000		75,000,000
Fair Value	(8,394,000)		(8,394,000)
Transaction Date December 2006, Interest Pay Rate 5.015%
Interest rate hedge agreements
Interest Pay Rate (as a percent)	5.015%		5.015%
Notional Amount	100,000,000		100,000,000
Effective	100,000,000		100,000,000
Fair Value	$ (6,243,000)		$ (6,243,000)