Summary of Significant Accounting Policies, Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities [Abstract]
Deferred tax liabilities	$ 18,236	$ 36,718
Reserve for other tax liabilities	14,382	7,163
Liability for deferred compensation plan	36,398	43,248
Pension plan benefits reserve	3,023	6,359
Build to suit - financing obligation	9,332	10,290
Deferred rent and deferred tenant incentives	5,665	6,389
Asset retirement obligation	6,444	6,578
Other	18,436	10,371
Total other liabilities	$ 111,916	$ 127,116