Derivatives and hedging activities (Details 5) (Recurring, USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Level 2
Assets at fair value:
Derivative financial instruments	$ 100	$ 1,394
Liabilities at fair value:
Derivative financial instruments	(11,093)	(15,683)
Total	(10,993)	(14,289)
Level 3
Liabilities at fair value:
Derivative financial instruments		(277)
Total		(277)
Fair Value
Assets at fair value:
Derivative financial instruments	100	1,394
Liabilities at fair value:
Derivative financial instruments	(11,093)	(15,960)
Total	$ (10,993)	$ (14,566)

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant