Income Taxes - Reconciliation from Statutory Federal Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation from statutory federal income taxes to the company's effective income taxes
Statutory federal income tax provision									$ 15,246	$ 45,729	$ 34,803
State taxes, net of federal income tax effect									4,757	15,764	12,724
Cash surrender life insurance									(1,163)	(565)	(582)
Tax exempt interest									(4,073)	(1,503)	(1,135)
Non-deductible merger costs									703	0	375
LIHTC investments									(2,259)	(1,570)	(761)
Effect of the Tax Act									0	0	(1,441)
Stock-based compensation shortfall (windfall) tax impact									407	(728)	(1,811)
Effect of the CARES Act									2,636	0	0
Section 162(m) of the Internal Revenue Code									968	530	145
Other									300	378	(77)
Total income tax provision	$ 22,800	$ 23,949	$ (40,324)	$ 5,825	$ 13,109	$ 15,492	$ 14,168	$ 15,266	$ 12,250	$ 58,035	$ 42,240