Summary of Significant Accounting Policies, Other Liabilities (Details) - USD ($) $ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Other Liabilities [Abstract] | ||
| Deferred tax liabilities | $ 10,741 | $ 18,236 |
| Reserve for other tax liabilities | 17,121 | 14,382 |
| Liability for deferred compensation plan | 43,238 | 36,398 |
| Pension plan benefits reserve | 3,454 | 3,023 |
| Build to suit - financing obligation | 0 | 9,332 |
| Deferred rent and deferred tenant incentives | 0 | 5,665 |
| Asset retirement obligation | 6,631 | 6,444 |
| Other | 15,610 | 18,436 |
| Total other liabilities | $ 96,795 | $ 111,916 |