Schedule of Repurchase Agreements Obligation by Type of Collateral Pledged (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	$ 207,676	$ 222,202
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 11. "Offsetting of Assets and Liabilities"	207,676	222,202
Amounts Related to Agreements Not Included in Offsetting Disclosure in Note 11. "Offsetting of Assets and Liabilities"	0	0
Overnight and Continuous \| Asset-backed Securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	0	0
Up to 30 Days \| Asset-backed Securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	42,034	42,908
30 - 90 Days \| Asset-backed Securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	131,448	144,731
Greater than 90 Days \| Asset-backed Securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	$ 34,194	$ 34,563

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