Fair Value Measurements - Narrative (Details) - Property |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2019 |
Dec. 31, 2018 |
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Impairment of lease, expiration period (or less) | 60 days | |
| Impaired long-lived assets held and used, properties | 1 | 8 |
| Number of impaired properties and buildings, long-lived assets held and used | 3 | |
| Impaired long-lived assets held for sale, properties | 9 | 1 |
| 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 | 1 | 5 |