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Equity-Based Compensation (Narrative) (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2015 | Sep. 30, 2015 | Sep. 30, 2014 | Dec. 31, 2013 | Jan. 31, 2015 | Jan. 31, 2014 | Jan. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Typical vesting period, in years |  | 4 years |  |  |  |  |
MSPP company matching portion, vesting age |  | 60 years |  |  |  |  |
Number of restricted stock units credited to participant accounts |  | 567,276 |  | 647,371 |  |  |
Disbursements of MSPP |  |  | $ 2,120,000 |  |  |  |
Former President and Chief Operating Officer |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Disbursements of MSPP | $ 1,686,000 |  |  |  |  |  |
2015 Equity Incentive Plan |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Maximum number of shares that may be issued under the Plan | 1,250,000 | 1,250,000 |  |  |  |  |
2005 Equity Incentive Plan |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Maximum number of shares that may be issued under the Plan | 274,374 | 274,374 |  |  |  |  |
Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Years of service |  | 5 years |  |  |  |  |
Average closing price, number of days trailing |  | 90 days |  |  |  |  |
Management Stock Purchase Plan |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Average closing price, number of days trailing |  | 200 days |  |  |  |  |
Accrues interest |  | 2.00% |  |  |  |  |
Number of restricted stock units credited to participant accounts |  | 91,873 | 116,708 |  |  |  |
Weighted average fair value of per unit awarded |  | $ 17.24 |  | $ 15.68 |  |  |
Minimum | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock unit vesting period |  | 1 year |  |  |  |  |
Maximum | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock unit vesting period |  | 3 years |  |  |  |  |
Unvested Restricted Stock Units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Number of restricted stock units credited to participant accounts |  | 58,052 |  | 62,455 |  |  |
Awarded January 2013 | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock units outstanding | 237,000 | 237,000 |  |  |  |  | 304,000
Performance stock unit grant-date fair value |  |  |  |  |  |  | $ 4,123,000
Percentage of target performance stock units earned |  | 50.00% |  |  |  |  |
Performance stock units earned |  | 114,000 |  |  |  |  |
Performance stock units target awards |  |  |  | 237,000 |  |  |
Awarded January 2014 | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock units outstanding | 224,000 | 224,000 |  |  |  | 212,000 |
Performance stock unit grant-date fair value |  |  |  |  |  | $ 3,914,000 |
Awarded June 2014 | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock units outstanding | 19,000 | 19,000 |  |  |  |  |
Performance stock unit grant-date fair value | $ 319,000 | $ 319,000 |  |  |  |  |
Awarded January 2015 | Performance stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Performance stock units outstanding |  |  |  |  | 219,000 |  |
Performance stock unit grant-date fair value |  |  |  |  | $ 4,039,000 |  |

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