Mortgage Loans (Details) - Loans receivable - Residential mortgage - Residential portfolio segment $ in Thousands	Jun. 30, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Number of Loans
Current | loan	14	17
Foreclosure | loan	46	67
Mortgage loans at fair value | loan	91	111
Fair Value and Carrying Value
Current	$ 1,493	$ 1,528
Foreclosure	6,879	8,874
Mortgage loans at fair value	9,778	11,477
Unpaid Principal Balance
Current	1,933	2,380
Foreclosure	14,487	18,813
Mortgage loans at fair value	24,178	29,350
Market Value of Underlying Properties
Current	2,813	3,156
Foreclosure	15,944	20,820
Mortgage loans at fair value	$ 26,065	$ 31,174
30
Number of Loans
Past Due | loan	3	1
Fair Value and Carrying Value
Past Due	$ 269	$ 51
Unpaid Principal Balance
Past Due	289	139
Market Value of Underlying Properties
Past Due	$ 613	$ 70
60
Number of Loans
Past Due | loan	2	3
Fair Value and Carrying Value
Past Due	$ 61	$ 304
Unpaid Principal Balance
Past Due	293	344
Market Value of Underlying Properties
Past Due	$ 239	$ 630
90
Number of Loans
Past Due | loan	26	23
Fair Value and Carrying Value
Past Due	$ 1,076	$ 720
Unpaid Principal Balance
Past Due	7,176	7,674
Market Value of Underlying Properties
Past Due	$ 6,456	$ 6,498