Employee Incentive Plans, Unrecognized Gross Compensation Cost Data Table (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended |
|---|---|
Sep. 30, 2011
years | |
Service-based vested and non-vested common shares and restricted stock units [Member] | |
| Unrecognized gross compensation cost data | |
| Unrecognized gross compensation costs, by award type | $ 4.5 |
| Expected period (in years) over which the remaining gross compensation costs will be recognized | |
| Expected period (in years) over which the remaining gross compensation costs will be recognized, by award type | 1.9 |
Performance Shares [Member] | |
| Unrecognized gross compensation cost data | |
| Unrecognized gross compensation costs, by award type | $ 4.7 |
| Expected period (in years) over which the remaining gross compensation costs will be recognized | |
| Expected period (in years) over which the remaining gross compensation costs will be recognized, by award type | 2.2 |