Mortgage-Backed Securities - Geographical and Other Statistics (Detail) - Non-agency MBS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Weighted average maturity (years)	20 years 8 months 12 days	21 years 7 months 6 days
Weighted average amortized loan to value	64.40%	66.50%
Weighted average FICO	697	698
Weighted average loan balance (in thousands)	$ 314	$ 319
Weighted average percentage owner occupied	84.40%	83.20%
Weighted average percentage single family residence	66.30%	65.80%
Weighted average current credit enhancement	2.20%	2.30%
California
Investment Holdings [Line Items]
Weighted average geographic concentration of top four states	31.70%	32.10%
New York
Investment Holdings [Line Items]
Weighted average geographic concentration of top four states	8.50%	7.90%
Florida
Investment Holdings [Line Items]
Weighted average geographic concentration of top four states	8.30%	8.10%
New Jersey
Investment Holdings [Line Items]
Weighted average geographic concentration of top four states	2.70%	2.70%

The weighted average maturity period of underlying mortgages, which is based on their current face amounts.

No definition available.

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- Definition

As of the balance sheet date, the weighted average of underlying mortgages at amortized cost to their fair values determined using defined pricing methodologies.

+ References

No definition available.

+ Details

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- Definition

As of the balance sheet date, the weighted average credit score of underlying mortgages based on their FICO ratings.

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No definition available.

+ Details

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- Definition

As of the balance sheet date, the percentage of unpaid principal amount of underlying mortgages originated in a specified territory.

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No definition available.

+ Details

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- Definition

As of the balance sheet date, the weighted average of unpaid principal amounts of underlying mortgages.

+ References

No definition available.

+ Details

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- Definition

As of the balance sheet date, the weighted average of underlying mortgages that are additionally secured in whole or in part with credit enhancements provided by third parties.

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No definition available.

+ Details

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- Definition

As of the balance sheet date, the weighted average of underlying mortgages that are owner occupied.

+ References

No definition available.

+ Details

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- Definition

As of the balance sheet date, the weighted average of underlying mortgages that are single family residences.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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