Fair Value Measurements (Fair Value of Senior Notes) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Senior Notes due 2021 at 4.875% [Member]
Carrying amount of senior notes	$ 496,998	$ 496,824
Estimated fair value of senior notes	529,450	533,150
Senior Notes due 2021 at 4.625% [Member]
Carrying amount of senior notes	299,519	299,493
Estimated fair value of senior notes	$ 315,360	$ 313,830

This element represents a certain statement of financial position liability caption which represents a class of liabilities, or which may include an individual liability, measured at fair value on a recurring basis.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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