Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value			$ 281
Fair Value Nonrecurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,618	$ 2,231	1,592
Total Gains/(Losses)	(871)	(595)	(302)
Fair Value Nonrecurring Basis [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,164	1,647	281
Total Gains/(Losses)	(808)	(505)	(294)
Fair Value Nonrecurring Basis [Member] | Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	454	584	1,311
Total Gains/(Losses)	(63)	(90)	(8)
Fair Value Nonrecurring Basis [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,618	2,231	1,592
Fair Value Nonrecurring Basis [Member] | Level 3 [Member] | Impaired Originated & PNCI Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,164	1,647	281
Fair Value Nonrecurring Basis [Member] | Level 3 [Member] | Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 454	$ 584	$ 1,311