Fair-Value Measurements (Narrative) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Senior unsecured notes	$ 1,050,604,000us-gaap_UnsecuredLongTermDebt	$ 1,050,639,000us-gaap_UnsecuredLongTermDebt
Long-term Debt, Fair Value	$ 1,000,000,000us-gaap_LongTermDebtFairValue	$ 1,000,000,000us-gaap_LongTermDebtFairValue

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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