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 (Parenthetical) (Detail) - USD ($)		Jul. 30, 2019	Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans		$ 26,408,000	$ 26,408,000	[1]	$ 27,534,000	[1]	$ 26,685,000	[1]
Troubled debt restructured loans	[2]		471,000		513,000		514,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans			3,906,000		3,840,000		4,329,000
Purchased Credit Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans			$ 464,000		$ 827,000		$ 2,813,000

[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.