Investment Securities (Available for Sale by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,086,386	$ 1,076,282
Fair value	1,083,601	$ 1,063,079
Available-for-sale Securities [Member]
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	3,005
Due after five years through ten years, amortized cost	25,976
Due after ten years, amortized cost	0
Amortized cost	28,981
Due in one year or less, fair value	0
Due after one year through five years, fair value	3,027
Due after five years through ten years, fair value	26,092
Due after ten years, fair value	0
Fair value	$ 29,119

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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