Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 472,039	$ 479,425
Fair value	479,827	$ 479,740
Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, amortized cost	10,605
Due after one year through five years, amortized cost	89,791
Due after five years through ten years, amortized cost	263,184
Due after ten years, amortized cost	108,289
Amortized cost	471,869
Due in one year or less, fair value	10,620
Due after one year through five years, fair value	90,661
Due after five years through ten years, fair value	267,797
Due after ten years, fair value	110,576
Fair value	$ 479,654

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

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