Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 461,738	$ 479,425
Fair value	476,698	$ 479,740
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	11,752
Due after one year through five years, amortized cost	99,205
Due after five years through ten years, amortized cost	252,531
Due after ten years, amortized cost	98,116
Amortized cost	461,604
Due in one year or less, fair value	11,768
Due after one year through five years, fair value	101,073
Due after five years through ten years, fair value	261,072
Due after ten years, fair value	102,648
Fair value	$ 476,561

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

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