Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, collectively evaluated for impairment	$ 6,078,069		$ 5,979,260
Financing receivable, allowance for credit losses, collectively evaluated for impairment	66,013		69,769
Financing receivable, individually evaluated for impairment and acquired with deteriorated credit quality	30,900
Financing receivable, allowance for credit losses, individually evaluated for impairment and acquired with deteriorated credit quality	1,200
Accrued interest receivable on loans	15,500		16,100
Financing receivable, allowance for credit loss	67,252	$ 48,884	71,124	$ 40,003
Provision for credit loss - securities	0	0
Debt securities, accrued interest after allowance for credit loss	4,400		3,300
Off-balance sheet, credit loss, liability	2,600		2,600
Off-balance sheet, credit loss, liability, credit loss expense (reversal)	24	210
Debt Securities, Allowance For Credit Loss	$ 144	$ 0	$ 2	0
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss				6,700
Off-balance sheet, credit loss, liability				(498)
Debt Securities, Allowance For Credit Loss				$ 30