Investment Securities - Contractual Maturities of Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year	$ 25,484
Due after one year through five years	252,960
Due after five years through ten years	250,865
Due after ten years	238,465
Residential mortgage-backed securities	1,306,625
Amortized Cost	2,074,399	$ 2,068,246
Fair Value
Due in one year	25,583
Due after one year through five years	257,616
Due after five years through ten years	260,318
Due after ten years	231,089
Residential mortgage-backed securities	1,292,364
Total investment securities held to maturity	$ 2,066,970	$ 2,034,943

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

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