Mortgage loans - Schedule of Loans (Details) - Loans receivable - Residential mortgage - Residential portfolio segment $ in Thousands	Jun. 30, 2016 USD ($) loan	Dec. 31, 2015 USD ($) loan
Number of loans
Current | loan	18	58
Foreclosure | loan	12	879
Mortgage loans | loan	32	1,297
Carrying value
Current	$ 1,864	$ 10,864
Foreclosure	1,587	225,024
Mortgage loans at fair value	4,058	317,336
Unpaid principal balance
Current	3,250	13,466
Foreclosure	2,118	314,991
Mortgage loans	5,988	440,366
Market value of underlying properties
Current	3,846	17,776
Foreclosure	2,399	330,573
Mortgage loans	$ 7,435	$ 465,007
30
Number of loans
Past Due | loan	2	26
Carrying value
Past Due	$ 607	$ 7,616
Unpaid principal balance
Past Due	620	10,013
Market value of underlying properties
Past Due	$ 1,190	$ 12,200
60
Number of loans
Past Due | loan		6
Carrying value
Past Due		$ 668
Unpaid principal balance
Past Due		775
Market value of underlying properties
Past Due		$ 1,063
90
Number of loans
Past Due | loan		328
Carrying value
Past Due		$ 73,164
Unpaid principal balance
Past Due		101,121
Market value of underlying properties
Past Due		$ 103,395
Nonperforming financing receivable
Number of loans
Current | loan	806	730
Foreclosure | loan	2,749	3,907
Mortgage loans | loan	4,072	5,739
Carrying value
Current	$ 133,230	$ 124,595
Foreclosure	502,238	687,464
Mortgage loans at fair value	707,445	960,534
Unpaid principal balance
Current	174,001	165,645
Foreclosure	682,067	946,962
Mortgage loans	962,517	1,355,554
Market value of underlying properties
Current	202,733	177,348
Foreclosure	685,175	917,671
Mortgage loans	$ 1,001,196	$ 1,322,606
Nonperforming financing receivable | 30
Number of loans
Past Due | loan	70	80
Carrying value
Past Due	$ 12,345	$ 12,003
Unpaid principal balance
Past Due	17,449	18,142
Market value of underlying properties
Past Due	$ 20,342	$ 21,858
Nonperforming financing receivable | 60
Number of loans
Past Due | loan	39	38
Carrying value
Past Due	$ 5,756	$ 5,688
Unpaid principal balance
Past Due	8,327	8,088
Market value of underlying properties
Past Due	$ 9,380	$ 8,766
Nonperforming financing receivable | 90
Number of loans
Past Due | loan	408	984
Carrying value
Past Due	$ 53,876	$ 130,784
Unpaid principal balance
Past Due	80,673	216,717
Market value of underlying properties
Past Due	$ 83,566	$ 196,963