Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost, debt securities held-to-maturity	$ 445,444	$ 453,629
Fair value	459,224	$ 467,966
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	9,461
Due after one year through five years, amortized cost	115,043
Due after five years through ten years, amortized cost	240,321
Due after ten years, amortized cost	80,602
Amortized cost, debt securities held-to-maturity	445,427
Due in one year or less, fair value	9,477
Due after one year through five years, fair value	117,204
Due after five years through ten years, fair value	248,418
Due after ten years, fair value	84,104
Fair value	$ 459,203

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

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