Fair Value Measurements (Details 1) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Long-term Debt [Member]
Other Fair Value Measurements
Other Fair Value Measurements	$ 366.7	$ 114.6
Unsecured Debt [Member]
Other Fair Value Measurements
Other Fair Value Measurements	$ 202.6	$ 203.0

Estimated fair value of the debt instrument at the balance-sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant