Mortgage Loans - Mortgage Loans (Details) - Loans receivable - Residential mortgage - Residential portfolio segment $ in Thousands	Sep. 30, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Number of Loans
Current | loan	19	20
Foreclosure | loan	20	36
Mortgage loans at fair value | loan	52	74
Fair Value and Carrying Value
Current	$ 1,520	$ 1,827
Foreclosure	1,616	5,481
Mortgage loans at fair value	3,613	8,072
Unpaid Principal Balance
Current	2,818	2,701
Foreclosure	5,481	12,376
Mortgage loans at fair value	12,225	21,244
Market Value of Underlying Properties
Current	4,409	4,353
Foreclosure	7,136	16,097
Mortgage loans at fair value	$ 15,543	$ 26,048
30 days past due
Number of Loans
Past Due | loan	2
Fair Value and Carrying Value
Past Due	$ 113
Unpaid Principal Balance
Past Due	195
Market Value of Underlying Properties
Past Due	$ 280
60 days past due
Number of Loans
Past Due | loan		1
Fair Value and Carrying Value
Past Due		$ 115
Unpaid Principal Balance
Past Due		148
Market Value of Underlying Properties
Past Due		$ 180
90 days past due
Number of Loans
Past Due | loan	11	17
Fair Value and Carrying Value
Past Due	$ 364	$ 649
Unpaid Principal Balance
Past Due	3,731	6,019
Market Value of Underlying Properties
Past Due	$ 3,718	$ 5,418