Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 439,303	$ 453,629
Fair value	460,587	$ 467,966
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	12,941
Due after one year through five years, amortized cost	118,220
Due after five years through ten years, amortized cost	232,672
Due after ten years, amortized cost	75,468
Amortized cost	439,301
Due in one year or less, fair value	13,018
Due after one year through five years, fair value	121,910
Due after five years through ten years, fair value	245,565
Due after ten years, fair value	80,089
Fair value	$ 460,582

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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