Fair Value Measurements Fair Value Measurements - Fair Values - Reported (Details) - USD ($) $ in Millions |
Sep. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Fair Value [Member] | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt | $ 711.1 | $ 635.6 |
| Carrying Value [Member] | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt | $ 748.3 | $ 635.0 |