Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Impaired Originated & PNCI Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 1,055		$ 281
Fair Value Nonrecurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,472	$ 1,308	1,592
Total Gains/(Losses)	(679)	(831)	(302)
Fair Value Nonrecurring Basis | Impaired Originated & PNCI Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,055	445	281
Total Gains/(Losses)	(652)	(808)	(294)
Fair Value Nonrecurring Basis | Foreclosed Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	417	863	1,311
Total Gains/(Losses)	(27)	(23)	(8)
Fair Value Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,472	1,308	1,592
Fair Value Nonrecurring Basis | Level 3 | Impaired Originated & PNCI Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	1,055	445	281
Fair Value Nonrecurring Basis | Level 3 | Foreclosed Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 417	$ 863	$ 1,311