Securities Sold Under Agreements to Repurchase - Schedule of Remaining Contractual Maturity of Secured Borrowings and Class of Collateral Pledged Under Repurchase Agreements (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets Sold Under Agreements To Repurchase [Line Items]
Secured borrowings and class of collateral pledged under repurchase agreements	$ 327,782	$ 362,294
U.S. Treasury [Member]
Assets Sold Under Agreements To Repurchase [Line Items]
Secured borrowings and class of collateral pledged under repurchase agreements	327,782
Overnight and Continuous [Member]
Assets Sold Under Agreements To Repurchase [Line Items]
Secured borrowings and class of collateral pledged under repurchase agreements	327,782
Overnight and Continuous [Member] | U.S. Treasury [Member]
Assets Sold Under Agreements To Repurchase [Line Items]
Secured borrowings and class of collateral pledged under repurchase agreements	$ 327,782