Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Due in one year	$ 26,173
Due after one year through five years	228,929
Due after five years through ten years	149,406
Due after ten years	199,307
Residential mortgage-backed securities	1,787,211
Amortized Cost	2,391,026	$ 2,173,011
Fair Value
Due in one year	26,306
Due after one year through five years	239,320
Due after five years through ten years	152,366
Due after ten years	197,628
Residential mortgage-backed securities	1,797,741
Total	$ 2,413,361	$ 2,227,612

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

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