Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Qualitative adjustments included in the ACL	$ 8,000
Increase (decrease) in ACL during period	(1,000)	$ 79,700
Provision for Credit Losses	315	25,382
Net charge-offs	1,300	1,300
Loans held for investment	13,117,392		$ 13,236,433
Off-balance sheet, credit loss, liability	32,800	11,600	$ 31,100
Provision for credit losses for off-balance sheet commitments	1,700	$ 72
Cumulative effect of the change in accounting principle
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for Credit Losses	$ 25,400
Loans held for investment				$ 55,700