Fair Value Measurements - Narrative (Details) - Property
|
6 Months Ended |
12 Months Ended |
Jun. 30, 2018 |
Dec. 31, 2017 |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Impaired long-lived assets held and used, properties |
2
|
18
|
| Impaired long-lived assets held for sale, properties |
|
8
|
| Fair Value Estimated Using Comparable Properties |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Impaired long-lived assets held and used, properties |
|
17
|
| Fair Value Estimated Using Listing Price or Broker Opinion of Value |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Impaired long-lived assets held and used, properties |
2
|
1
|