Debt - Additional Information (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2016 |
Jun. 30, 2017 |
Jun. 30, 2016 |
|
| Debt Instrument [Line Items] | ||||
| Cash payments paid for interest | $ 48.1 | $ 43.1 | ||
| Amortization of treasury lock settlements | $ 1.4 | $ 1.4 | 2.8 | 2.8 |
| Amortization of deferred financing costs | 0.5 | $ 0.5 | 1.0 | $ 0.9 |
| Unsecured Debt | Five-Year Term Loan, due August 2021 | ||||
| Debt Instrument [Line Items] | ||||
| Repayment of debt | $ 29.8 | |||
| Debt instrument, term | 5 years | |||
| Unsecured Debt | Seven-Year Term Loan, due October 2020 | ||||
| Debt Instrument [Line Items] | ||||
| Repayment of debt | $ 3.3 | |||
| Debt instrument, term | 7 years | |||
| Senior Notes | Fixed-Rate Senior Notes | ||||
| Debt Instrument [Line Items] | ||||
| Book value of fixed rate debt | 1,647.7 | $ 1,647.7 | ||
| Long-term debt (fixed-rate debt), fair value | 1,740.4 | 1,740.4 | ||
| Term Loan | Variable-Rate Term Loans | ||||
| Debt Instrument [Line Items] | ||||
| Book value of variable rate debt | $ 977.6 | $ 977.6 | ||