Asset Acquisitions and Dispositions - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) loan property	Sep. 30, 2018 USD ($) loan property	Sep. 30, 2019 USD ($) loan property	Sep. 30, 2018 USD ($) loan property
Real Estate [Line Items]
Cash paid in acquisition of real estate			$ 11,124	$ 475,276
Number of real estate properties sold | property	126	72	862	402
Proceeds from dispositions of real estate			$ 169,457	$ 73,468
Proceeds from sale and resolution of mortgage loans	$ 200	$ 800	$ 1,800	$ 2,700
Nonperforming financing receivable | Residential mortgage | Loans receivable
Real Estate [Line Items]
Number of mortgage loans resolved | loan	5	5	18	26
One-By-One Acquisition Program
Real Estate [Line Items]
Number of real estate properties directly acquired | loan	28	12	85	66
Cash paid in acquisition of real estate	$ 3,800	$ 1,600	$ 11,100	$ 8,300
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate [Line Items]
Proceeds from dispositions of real estate	$ 22,600	$ 10,900	$ 175,800	$ 71,100