Commitments and Contingencies - Contractual amount of off-balance sheet instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments to extend credit
Financial instruments whose contract amounts represent credit risk:
Financial instruments	$ 2,993,692	$ 2,126,275
Letters of credit
Financial instruments whose contract amounts represent credit risk:
Financial instruments	$ 32,702	$ 22,533