Loans and Allowance for Credit Losses for Loans - Summary of Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Receivables [Abstract]
Allowance for loan losses	$ 325,032	$ 309,614	$ 161,759	$ 161,853	$ 155,105	$ 151,859
Allowance for unfunded credit commitments	10,296		2,845
Total allowance for credit losses	$ 335,328		$ 164,604

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant