Investment Securities (Available for Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 915,518	$ 965,135
Fair value	948,614	$ 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	3,655
Due after five years through ten years, amortized cost	25,255
Due after ten years, amortized cost	2,000
Amortized cost	30,910
Due in one year or less, fair value	0
Due after one year through five years, fair value	3,820
Due after five years through ten years, fair value	25,805
Due after ten years, fair value	2,004
Fair value	$ 31,629

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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