Mortgage-Backed and Credit Risk Transfer Securities - Components of MBS and GSE CRT Interest Income (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	$ 166,319	$ 146,069
Net (Premium Amortization)/Discount Accretion	(17,316)	(27,196)
Interest Income	149,003	118,873
Agency
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	108,317	91,231
Net (Premium Amortization)/Discount Accretion	(23,222)	(28,578)
Interest Income	85,095	62,653
CMBS
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	37,293	29,676
Net (Premium Amortization)/Discount Accretion	1,426	(2,634)
Interest Income	38,719	27,042
Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	14,012	20,614
Net (Premium Amortization)/Discount Accretion	5,177	4,387
Interest Income	19,189	25,001
GSE CRT
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	6,525	4,487
Net (Premium Amortization)/Discount Accretion	(697)	(371)
Interest Income	5,828	4,116
Other
Schedule of Available-for-sale Securities [Line Items]
Coupon Interest	172	61
Net (Premium Amortization)/Discount Accretion	0	0
Interest Income	$ 172	$ 61

Marketable Securities Coupon Interest

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- Definition

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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- Definition

Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895926&loc=d3e24721-111560

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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.

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