Condensed Financial Information of Registrant Condensed Financial Information of Registrant - Guarantee (Details) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Aug. 31, 2011	Aug. 31, 2010
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Maximum borrowing capacity under credit agreement	$ 800,000,000	$ 125,000,000	$ 100,000,000
Voting equity guarantee on indebtedness, percentage	65.00%
Non-voting guarantee on indebtedness, percentage	100.00%

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 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 2: 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