Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 446,591	$ 453,629
Fair value	467,693	$ 467,966
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	22,685
Due after one year through five years, amortized cost	130,032
Due after five years through ten years, amortized cost	221,305
Due after ten years, amortized cost	72,569
Amortized cost	446,591
Due in one year or less, fair value	22,792
Due after one year through five years, fair value	134,202
Due after five years through ten years, fair value	234,041
Due after ten years, fair value	76,658
Fair value	$ 467,693

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

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