Debt Obligations (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Debt Instrument [Line Items]
Senior secured revolving credit facility	$ 150
Letter of Credit Sublimit [Member] \| Credit Agreement Before Amended [Member]
Debt Instrument [Line Items]
Senior secured revolving credit facility	50
Letter of Credit Sublimit [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Senior secured revolving credit facility	100
Swingline Commitment [Member]
Debt Instrument [Line Items]
Senior secured revolving credit facility	10
Prior Credit Agreement [Member]
Debt Instrument [Line Items]
Senior secured revolving credit facility	$ 100
Line of credit facility, initiation date	Oct. 16, 2008
Line of credit facility, expiration date	Oct. 16, 2011

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant