Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 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	$ 212		$ 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	426	$ 2,877	1,592
Total Gains/(Losses)	(99)	(882)	(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	212	2,103	281
Total Gains/(Losses)	(197)	(795)	(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	214	774	1,311
Total Gains/(Losses)	98	(87)	(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	426	2,877	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	212	2,103	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	$ 214	$ 774	$ 1,311