Investment Securities (Available for Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 955,485	$ 965,135
Fair value	989,833	$ 976,919
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	0
Due after one year through five years, amortized cost	3,002
Due after five years through ten years, amortized cost	25,922
Due after ten years, amortized cost	0
Amortized cost	28,924
Due in one year or less, fair value	0
Due after one year through five years, fair value	3,040
Due after five years through ten years, fair value	26,616
Due after ten years, fair value	0
Fair value	$ 29,656

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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