Incentive Award Plan - Narrative (Details) - USD ($)
shares in Thousands, $ in Millions |
3 Months Ended |
|
Mar. 31, 2019 |
Mar. 31, 2018 |
Dec. 31, 2018 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Unamortized stock-based compensation expense |
$ 22.4
|
|
$ 15.5
|
| General and administrative expense |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Stock-based compensation expense |
3.6
|
$ 4.4
|
|
| Non-vested Shares of Restricted Stock |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Deferred compensation expense |
$ 5.7
|
|
|
| Outstanding unvested shares |
436
|
|
|
| Unamortized stock-based compensation expense |
$ 11.6
|
|
8.1
|
| Performance Shares |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Number of shares available for grant |
97
|
|
|
| Volatility rate |
25.40%
|
|
|
| Minimum required service period |
3 years
|
|
|
| Dividend rights accrued |
$ 2.0
|
|
1.7
|
| Potential grants in period based on total shareholder return (in shares) |
200
|
|
|
| Unamortized stock-based compensation expense |
$ 10.8
|
|
$ 7.4
|
| Performance Shares | Minimum |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Multiplier for shares granted |
0.00%
|
|
|
| Performance Shares | Maximum |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Multiplier for shares granted |
250.00%
|
|
|
| Executives Officers and Employees | Non-vested Shares of Restricted Stock |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Grants in period (in shares) |
149
|
|
|
| Group of Industry Peers | Performance Shares |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Volatility rate, minimum |
15.30%
|
|
|
| Volatility rate, maximum |
30.80%
|
|
|