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.

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Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Repurchase Agreements - Summary of Repurchase Agreements (Parenthetical) (Detail) - Bond	Sep. 30, 2019	Dec. 31, 2018
Barclays MRA [Member]
Debt Instrument [Line Items]
Number of corporate bond		1
RBC MRA [Member]
Debt Instrument [Line Items]
Number of corporate bond	10
BAML MRA [Member]
Debt Instrument [Line Items]
Number of corporate bond	1