Derivative Instruments and Hedging Activities (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2012
Derivative Instruments and Hedging Activities
Ineffectiveness recognized during the period	$ 0	$ 0
Derivatives reclassified as increase to interest expense			12,800,000
Fair value of derivative net liability position	13,100,000	13,100,000
Derivative counterparty posted collateral against obligation	$ 20,500,000	$ 20,500,000

The amount of net gains or losses on a cash flow hedge reclassified in the period to interest expense from accumulated other comprehensive income.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80784-113994

Name:	us-gaap_CashFlowHedgeGainLossReclassifiedToInterestExpenseNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration