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