Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-Section 50
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Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
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The cash inflow from the maturity (principal due), prepayment and call (request of early payment) of a loan financed by home mortgage payments classified as held to maturity.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
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Amount of cash inflow from sale of investment in mortgage-backed security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Mortgage-Backed Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Sale of securities	$ 63,270	$ 35,324	$ 2,303,025	$ 624,397
Unrealized gain (loss) on trading investments	1,900	3,000	17,800	(14,600)
Agency MBS
Schedule Of Available For Sale Securities [Line Items]
Sale of securities	59,600	35,300	2,300,000	618,500
Gross realized losses on sales of securities	3	200	20,500	19,500
Gross realized gains on sales of securities	448	600	8,100	600
Unrealized gain (loss) on trading investments	1,939	(3,017)	17,834	(14,584)
Non-Agency MBS
Schedule Of Available For Sale Securities [Line Items]
Sale of securities	3,700		23,700
Securities called		36,100
Gross realized losses on sales of securities	$ 231		231	42
Gross realized gains on sales of securities		$ 200	22	217
Trading Securities \| Agency MBS
Schedule Of Available For Sale Securities [Line Items]
Unrealized gain (loss) on trading investments			$ 1,900		$ (15,900)
Non-Agency MBS
Schedule Of Available For Sale Securities [Line Items]
Sale of securities				$ 41,900