Assets Measured at Fair Value on Non-Recurring Basis (Detail) - Fair Value, Measurements, Non-Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 16,318	$ 13,217
Total (Losses) Gains Recognized	(939)	1,978
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	16,318	13,217
Impaired loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	16,198	10,085
Total (Losses) Gains Recognized	(937)	1,972
Impaired loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	16,198	10,085
Other real estate owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	120	3,132
Total (Losses) Gains Recognized	(2)	6
Other real estate owned [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 120	$ 3,132