Real Estate Assets, Net - Narrative (Details) $ in Thousands	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2018 USD ($) property		Sep. 30, 2017 USD ($) property	Sep. 30, 2018 USD ($) property		Sep. 30, 2017 USD ($) property	Dec. 31, 2017 USD ($) property		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Real Estate [Line Items]
Number of properties owned | property				17			14
Aggregate carrying value REO properties	$ 8,100			$ 8,100
Number of REO properties held for rental | property				12			5
Rental property, net	8,080			$ 8,080			$ 1,284
Number of real estate properties purchased | property				1			1
Number of properties acquired through foreclosure | property				1			3
Number of properties transferred from property held for sale | property				12			10
Impaired REO held for sale net at NRV	20,463	[1]	$ 27,342	$ 20,463	[1]	$ 27,342	$ 24,947	[1]	$ 22,807	$ 28,278	$ 23,882
Real estate properties undergoing renovation	$ 700			$ 700			$ 1,800
Number of held-for-sale residential properties disposed | property	32		28	93		92
Gain (loss) on sale of property				$ 264		$ 170
Real estate operating expense	$ 900		$ 1,100	2,000		2,000
Other Income
Real Estate [Line Items]
Gain (loss) on sale of property	$ (200)		$ 100	$ 300		$ 100
Multi-family apartment building
Real Estate [Line Items]
Number of real estate properties | property	2			2
Rental property, net	$ 5,000			$ 5,000
commercial building
Real Estate [Line Items]
Number of real estate properties | property	1			1
Rental property, net	$ 800			$ 800

[1] Property held-for-sale, net, includes valuation allowances of $2.0 million and $1.8 million at September 30, 2018 and December 31, 2017, respectively.