Marketable Securities (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Marketable Securities
Unrealized loss through accumulated other comprehensive income or loss	$ 0.2

The increase (decrease), resulting in a loss, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

No definition available.

Name:	us-gaap_UnrealizedLossOnSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration