Fair-Value Measurements (Narrative) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
7.875% senior unsecured notes (including unamortized premium of $639 and $772 in 2014 and 2013, respectively)	$ 1,050,639,000us-gaap_UnsecuredLongTermDebt	$ 700,772,000us-gaap_UnsecuredLongTermDebt
Fair value of debt	1,003,600,000us-gaap_LongTermDebtFairValue	732,400,000us-gaap_LongTermDebtFairValue
Seven Point Eight Seventy Five Percentage Senior Unsecured Notes [Member]
7.875% senior unsecured notes (including unamortized premium of $639 and $772 in 2014 and 2013, respectively)	$ 350,639,000	$ 350,772,000

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