Loans Held for Investment and Allowance for Credit Losses on Loans - Carrying Amount of Purchased Credit Deteriorated Loans (Detail) - Financial Asset Acquired with Credit Deterioration [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Financing Receivable Allowance For Credit Losses [Line Items]
Purchase price of loans at acquisition	$ 1,761
Allowance for credit losses at acquisition	502
Par value of acquired loans at acquisition	$ 2,263