Real Estate Securities - Additional Information (Details)	12 Months Ended
Dec. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment
Investment Holdings [Line Items]
Trading securities	$ 445,687,000	$ 404,011,000
Trading securities acquired	307,000,000	383,000,000
Trading securities sold	241,000,000	18,000,000
Change in trading securities	11,000,000	(17,000,000)
Trading securities pledged as collateral	146,000,000
AFS securities acquired	35,000,000	33,000,000
AFS securities sold	253,000,000	366,000,000
AFS net realized gains	$ 21,000,000	$ 34,000,000
Number of AFS securities \| Investment	186	224
Number of securities in unrealized loss position \| Investment	19	32
Number of securities in a continuous unrealized loss position for twelve consecutive months or longer \| Investment	10	15
Other than temporary impairments	$ 3,000,000	$ 400,000
Other than temporary impairment losses, income statement	400,000	200,000
Accumulated other comprehensive income, other-than-temporary impairments	3,000,000	200,000
Residential
Investment Holdings [Line Items]
Gross unrealized losses	3,169,000	5,007,000
Residential
Investment Holdings [Line Items]
Marketable securities, less than five years	1,000,000
Marketable securities, due from five to ten years	1,000,000
Interest Only Securities
Investment Holdings [Line Items]
Trading securities	37,000,000	37,000,000
Residential Senior and Subordinate Securities \| Trading securities
Investment Holdings [Line Items]
Unpaid principal balance	0	217,000,000
Residential Subordinate Securities \| Trading securities
Investment Holdings [Line Items]
Unpaid principal balance	434,000,000	168,000,000
Subordinate Securities
Investment Holdings [Line Items]
Trading securities	408,620,000	149,660,000
Subordinate Securities \| Residential
Investment Holdings [Line Items]
Gross unrealized losses	1,240,000	1,430,000
Subordinate Securities \| Credit Risk Transfer (CRT) Securities
Investment Holdings [Line Items]
Trading securities	187,000,000	48,000,000
Subordinate Securities \| Sequoia Securities
Investment Holdings [Line Items]
Trading securities	15,000,000	10,000,000
Subordinate Securities \| Other Third Party Securities
Investment Holdings [Line Items]
Trading securities	115,000,000	83,000,000
Subordinate Securities \| Commercial Mortgage Backed Securities
Investment Holdings [Line Items]
Trading securities	92,000,000	8,000,000
AFS Securities \| Residential
Investment Holdings [Line Items]
Securities pledged as collateral	$ 216,000,000
Re-REMIC
Investment Holdings [Line Items]
Number of AFS securities \| Investment	4
Trading securities, fair value	$ 77,000,000
Re-REMIC \| Residential
Investment Holdings [Line Items]
Gross unrealized losses	$ 0	$ 0

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Number of Securities, Continuous Unrealized Loss Position More Than Twelve Months

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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