Loans Held for Investment and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Detail) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Receivables [Abstract]
Non-accrual loans	[1]	$ 39,320	$ 24,582	$ 26,408
Loans still accruing and past due 90 days or more		92	153	300
Troubled debt restructured loans still accruing	[2]	25	26	471
Total		$ 39,437	$ 24,761	$ 27,179

[1] Includes $7,275,000, $464,000 and $251,000 of purchased credit impaired loans as of June 30, 2020 and 2019, and December 31, 2019, respectively.

[2] Troubled debt restructured loans of $4,673,000, $3,906,000 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 June 30, 2020 and 2019, and December 31, 2019, respectively.