Stockholders' Equity and Equity Instruments - Narrative (Details) - USD ($)
$ in Millions |
9 Months Ended |
12 Months Ended |
|
Sep. 30, 2018 |
Sep. 30, 2017 |
Dec. 31, 2017 |
May 31, 2015 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Reissued shares of treasury stock (in shares) |
5,665
|
|
|
|
| Treasury stock reissued (in shares) |
|
|
38,197
|
|
| Tax deficiency from equity compensation awards recorded as an increase to income tax expense |
$ 0.5
|
|
|
|
| Compensation expense recorded during period pursuant to stock-based compensation plans |
$ 3.6
|
$ 3.8
|
|
|
| Stock Options |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Vesting period |
4 years
|
|
|
|
| Options expiration period |
7 years
|
|
|
|
| Number of shares available from conversion (in shares) |
1
|
|
|
|
| Reissued shares of treasury stock (in shares) |
0
|
|
|
|
| RSUs |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Vesting period |
3 years
|
|
|
|
| Number of shares available from conversion (in shares) |
1
|
|
|
|
| Service period |
3 years
|
|
|
|
| Reissued shares of treasury stock (in shares) |
15,080
|
|
|
|
| TSR PSUs |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Performance period of PSUs |
3 years
|
|
|
|
| TSR PSUs | Minimum |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Percentage of shares earned |
0.00%
|
|
|
|
| TSR PSUs | Maximum |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Percentage of shares earned |
150.00%
|
|
|
|
| ROIC PSUs |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Performance period of PSUs |
3 years
|
|
|
|
| ROIC PSUs | Minimum |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Percentage of shares earned |
0.00%
|
|
|
|
| ROIC PSUs | Maximum |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Percentage of shares earned |
200.00%
|
|
|
|
| PSUs |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Reissued shares of treasury stock (in shares) |
2,753
|
|
|
|
| 2015 Incentive Award Plan |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Shares authorized for issuance (in shares) |
|
|
|
3,000,000
|