Investment Securities - Contractual Maturities of Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Due in one year	$ 23,737
Due after one year through five years	247,505
Due after five years through ten years	220,403
Due after ten years	241,209
Residential mortgage-backed securities	1,360,903
Amortized Cost	2,093,757	$ 2,068,246
Fair Value
Due in one year	23,760
Due after one year through five years	254,040
Due after five years through ten years	230,852
Due after ten years	237,726
Residential mortgage-backed securities	1,374,825
Total investment securities held to maturity	$ 2,121,203	$ 2,034,943

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

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