Fair Value Measurements (Fair Value of Senior Notes) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
4.875% Senior Notes due 2021 [Member]
Carrying amount of senior notes	$ 498,052	$ 497,876
Estimated fair value of senior notes	543,999	566,700
4.625% Senior Notes due 2021 [Member]
Carrying amount of senior notes	299,676	299,650
Estimated fair value of senior notes	323,712	337,222
3.800% Senior Notes due 2022 [Member]
Carrying amount of senior notes	299,160	299,109
Estimated fair value of senior notes	303,234	310,749
3.850% Senior Notes due 2023 [Member]
Carrying amount of senior notes	299,980	299,980
Estimated fair value of senior notes	$ 300,559	$ 311,656

Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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

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