Summary of Significant Accounting Policies - Goodwill (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill		$ 1,337,773	$ 1,337,773
Goodwill allocated to dispositions and held for sale assets	$ 73,200
Properties foreclosed upon [Member]
Goodwill [Line Items]
Goodwill allocated to dispositions and held for sale assets	$ 2,300
Mortgages [Member]
Goodwill [Line Items]
Number of properties foreclosed upon | property	2