Investment Securities - Contractual Maturities of Investments Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year	$ 4,666
Due after one year through five years	125,825
Due after five years through ten years	78,305
Due after ten years	118,549
Total investment securities available for sale	1,796,404	$ 1,511,034
Fair Value
Due in one year	4,643
Due after one year through five years	123,051
Due after five years through ten years	76,640
Due after ten years	115,428
Total investment securities available for sale	1,749,544	1,493,905
Residential mortgage-backed securities
Amortized Cost
Securities without a single maturity date	1,469,059
Total investment securities available for sale	1,469,059	1,239,534
Fair Value
Securities without a single maturity date	1,429,782
Total investment securities available for sale	$ 1,429,782	$ 1,223,295

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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