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		Jul. 30, 2019	Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Receivables [Abstract]
Non-accrual loans		$ 26,408	$ 26,408	[1]	$ 27,534	[1]	$ 26,685	[1]
Loans still accruing and past due 90 days or more			300		1,008		200
Troubled debt restructured loans	[2]		471		513		514
Total			$ 27,179		$ 29,055		$ 27,399

[1] Includes $464,000, $2,813,000 and $827,000 of purchased credit impaired loans as of June 30, 2019 and 2018, and December 31, 2018, respectively.

[2] Troubled debt restructured loans of $3,906,000, $4,329,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans at June 30, 2019 and 2018, and December 31, 2018, respectively.