Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Details) $ in Thousands	Mar. 31, 2021 USD ($)
Amortized Cost
Less than one year	$ 105,213
Due after one year through five years	189,783
Due after five years through ten years	164,010
Due after ten years	157,741
Total amortized cost	616,747
Estimated Fair Value
Less than one year	105,784
Due after one year through five years	194,363
Due after five years through ten years	162,249
Due after ten years	162,536
Total estimated fair value	$ 624,932