Investments - Summary of Gross Real Estate and Loan Activity (Footnote) (Details) - USD ($)
$ in Millions |
12 Months Ended |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Real Estate [Abstract] |
|
|
|
| Revenue producing capitalized expenditures |
$ 46.0
|
$ 42.6
|
|
| Non-revenue producing capitalized maintenance expenditures |
6.3
|
3.5
|
|
| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations |
|
|
|
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
|
|
|
| Accumulated depreciation and amortization associated with dispositions of real estate |
19.5
|
57.1
|
|
| Discontinued Operations, Held-for-use |
|
|
|
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
|
|
|
| Gain on disposal of assets for properties |
1.4
|
24.6
|
$ 35.8
|
| Discontinued Operations, Held-for-sale |
|
|
|
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
|
|
|
| Gain on disposal of assets for properties |
$ 13.0
|
$ 40.5
|
$ 16.6
|