Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Zenith Acquisition [Member]
Subsequent Event [Line Items]
Subsequent Event, Amount	$ 127
Short Term Credit Agreement [Member]
Subsequent Event [Line Items]
Subsequent Event, Amount	$ 25
Amended and Restated Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Minimum proceeds from issuance of equity securities to be applied to repay borrowings outstanding under term loan (in hundredths)	50.00%

Reflects the known or estimated financial effect of the event, or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued.

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

-Publisher FASB

-Topic 855

-SubTopic 10

-Section 50

-Paragraph 2

-Name Accounting Standards Codification

-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 165

-Paragraph 13

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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