Summary of Significant Accounting Policies (Details 2) (Interest rate contracts, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Revolving credit facility
Derivative instruments
Notional amount of outstanding derivative instruments	$ 100.0		$ 100.0
Cash Flow Hedging
Derivative instruments
Notional amount of outstanding derivative instruments	100.0
Net fair value of swap liability	1.2		1.7
Interest expenses	$ 0.4	$ 2.4