Loans Held for Investment and Allowance for Credit Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Detail) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Receivables [Abstract]
Non-accrual loans	[1]	$ 39,226	$ 24,582	$ 28,508
Loans still accruing and past due 90 days or more		209	153	97
Troubled debt restructured loans	[2]	26	26	472
Total		$ 39,461	$ 24,761	$ 29,077

[1] Includes $7,773,000, $859,000 and $251,000 of purchased credit impaired loans as of March 31, 2020 and 2019, and December 31, 2019, respectively.

[2] Troubled debt restructured loans of $4,733,000, $4,566,000 and $4,791,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans at March 31, 2020 and 2019, and December 31, 2019, respectively.