Core Deposit Intangibles - Schedule of Core Deposit and Other Intangibles (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 102,396	$ 85,869
Accumulated amortization	(71,945)	(67,434)
Total core deposit intangibles	30,451	34,962
Core deposit intangibles acquired
Finite-Lived Intangible Assets [Line Items]
Core deposit intangibles acquired	$ 0	$ 16,527