Loans Held for Investment and Allowance for Credit Losses on Loans - Transfers from Loans and Premises and Equipment to Other Real Estate Owned, Repossessed Assets and Other Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncash Investing And Financing Items [Abstract]
Other real estate owned	$ 32,093	$ 3,941	$ 5,437
Repossessed assets	1,418	1,473	1,122
Other assets	11,105
Total	$ 44,616	$ 5,414	$ 6,559