Fair Value Measurements - Narrative (Details) - Property |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2017 |
Dec. 31, 2016 |
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Impaired long-lived assets held and used, properties | 16 | 33 |
| Impaired long-lived assets held and used, properties estimating fair values on comparable properties | 15 | 16 |
| Weighted Average Listing Price or Broker Opinion of Value Per Square Foot | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Impaired long-lived assets held and used, properties | 1 | 17 |