Derivative Instruments and Hedging Activities (Details) (Interest Rate Swap, USD $) In Millions, unless otherwise specified | 9 Months Ended |
|---|---|
Sep. 30, 2011 | |
| Derivative | |
| Derivatives, Expected net loss to be transferred from accumulated OCI to earnings within 12 months | $ 15.1 |
Designated as Hedging Instrument | |
| Derivative | |
| Derivative, Net Liability Position, Aggregate Fair Value | 26.9 |
Swaps Effective February 2010 | |
| Derivative | |
| Notional Amount of Interest Rate Derivatives | 1,000.0 |
| Derivative, Weighted Average Fixed Interest Rate | 5.927% |
| Derivative, Maturity Date | Feb. 01, 2012 |
Swaps Effective February 2012 | |
| Derivative | |
| Notional Amount of Interest Rate Derivatives | 950.0 |
| Derivative, Weighted Average Fixed Interest Rate | 4.933% |
| Derivative, Maturity Date | Feb. 01, 2014 |
Swaps Effective April 2011 | |
| Derivative | |
| Notional Amount of Interest Rate Derivatives | $ 450.0 |
| Derivative, Weighted Average Fixed Interest Rate | 5.242% |
| Derivative, Maturity Date | Apr. 15, 2014 |