Investment Securities (Disclosure Regarding Length of Time on Investment Securities with Temporary Impairment) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, fair value	$ 16,140	$ 96,412
Less than 12 months, gross unrealized losses	(159)	(918)
12 months or longer, fair value	54,654	95,192
12 months or longer, gross unrealized losses	(926)	(3,101)
Total, fair value	70,794	191,604
Total, gross unrealized losses	(1,085)	(4,019)
Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, fair value	3,652	0
Less than 12 months, gross unrealized losses	(56)	0
12 months or longer, fair value	0	4,525
12 months or longer, gross unrealized losses	0	(94)
Total, fair value	3,652	4,525
Total, gross unrealized losses	(56)	(94)
State And Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, fair value	4,357	96,412
Less than 12 months, gross unrealized losses	(31)	(918)
12 months or longer, fair value	54,654	81,663
12 months or longer, gross unrealized losses	(926)	(2,849)
Total, fair value	59,011	178,075
Total, gross unrealized losses	(957)	(3,767)
Corporate Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, fair value	8,131	0
Less than 12 months, gross unrealized losses	(72)	0
12 months or longer, fair value	0	9,004
12 months or longer, gross unrealized losses	0	(158)
Total, fair value	8,131	9,004
Total, gross unrealized losses	$ (72)	$ (158)