Stock-Based Compensation Plans - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions |
3 Months Ended |
9 Months Ended |
12 Months Ended |
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Dec. 31, 2015 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Performance-based shares earned |
|
|
|
|
142,256
|
| Stock-based compensation cost |
$ 1.9
|
$ 2.7
|
$ 5.5
|
$ 6.7
|
|
| Total unrecognized compensation cost related to non-vested share-based compensation arrangements |
$ 8.2
|
|
$ 8.2
|
|
|
| Compensation cost not yet recognized, period for recognition |
|
|
1 year 6 months 2 days
|
|
|
| Restricted Stock Units |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Granted, number of shares |
|
|
124,077
|
124,170
|
|
| Grants in period, weighted average grant date fair value (in dollars per share) |
|
|
$ 38.21
|
$ 32.47
|
|
| Performance Shares |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Granted, number of shares |
|
|
156,576
|
|
180,526
|
| Grants in period, weighted average grant date fair value (in dollars per share) |
|
|
$ 38.47
|
|
$ 32.60
|