Derivative Financial Instruments (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2012
Derivative [Line Items]
Interest rate swap contracts outstanding notional amounts	935,000
Interest Rate Swap Contracts Effective In July 2012 [Member]
Derivative [Line Items]
Interest rate swap contracts outstanding notional amounts	200,000
Minimum [Member]
Derivative [Line Items]
Interest rate swap contracts maturity date	September 2015
Maximum [Member]
Derivative [Line Items]
Interest rate swap contracts maturity date	July 2017

Aggregate notional amount of all derivatives designated as cash flow hedging instruments. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Name:	us-gaap_NotionalAmountOfCashFlowHedgeInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant