Fair Value (Details Textual) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Fair Value (Additional Textual) [Abstract]
Maximum maturity period of cash and cash equivalent	three months or less
Maturity period of short-term investments	four months and one year
Long-term fixed-rate debt, fair value	$ 492.5	$ 480.7
Long-term fixed-rate debt, carrying value	$ 427.2	$ 428.9

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

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