Investment Securities - Contractual Maturities of Debt Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due in one year	$ 20,975
Due after one year through five years	92,873
Due after five years through ten years	107,004
Due after ten years	66,062
Residential mortgage-backed securities	1,193,052
Amortized Cost	1,479,966	$ 1,558,787
Fair Value
Due in one year	20,991
Due after one year through five years	95,436
Due after five years through ten years	108,746
Due after ten years	67,955
Residential mortgage-backed securities	1,233,436
Total investment securities available for sale	$ 1,526,564	$ 1,566,801

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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