Loans Held for Investment and Allowance for Loan Losses - Recorded Investment in Impaired Loans and Related Valuation Allowance (Detail) - USD ($) $ in Thousands	Jul. 30, 2019	Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Receivables [Abstract]
Recorded Investment	$ 26,408	$ 26,408	[1]	$ 27,534	[1]	$ 26,685	[1]
Valuation Allowance		$ 3,866		$ 4,069		$ 4,823

[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.