Derivative Instruments (Details) (Interest rate swaps [Member], Interest Expense [Member], Cash Flow Hedge [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Interest rate swaps [Member] \| Interest Expense [Member] \| Cash Flow Hedge [Member]
Effects of changes in the fair values of derivatives designated as cash flow hedges on the accompanying Condensed Consolidated Statements of Comprehensive Income
Loss reclassified from AOCI (effective portion)	$ (1,575)	$ (1,995)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Name:	us-gaap_CashFlowHedgeLossReclassifiedToInterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration