Goodwill, Deferred Leasing Costs and Other Intangibles - Goodwill By Reportable Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 851,757	$ 1,452,891	$ 1,374,809	$ 1,514,561
Goodwill deductible for tax purposes	140,500	140,500
Digital Operating
Goodwill [Line Items]
Goodwill	471,948	479,082
Digital Investment Management
Goodwill [Line Items]
Goodwill	298,248	247,248
Other
Goodwill [Line Items]
Goodwill	$ 81,561	$ 726,561