Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified			3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Interest Rate Swaps One [Member]	Mar. 31, 2012 Interest Rate Swaps Two [Member]	Mar. 31, 2012 Interest Rate Swaps Three [Member]	Mar. 31, 2012 Interest Rate Swaps Four [Member]
Information regarding the Swaps
Notional amount of interest rate derivatives	$ 383.8	$ 284.1	$ 100.0	$ 83.8	$ 100.0	$ 100.0
LIBOR Fixed Rate			1.00%	2.80%	1.60%	1.50%
Maturity date			Jun. 30, 2014	Sep. 30, 2017	Feb. 28, 2019	Feb. 28, 2019