Organization - Narrative (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) loan_pool bank_branch loan_segment loan_class model	Sep. 30, 2019 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Number of loan segments | loan_segment					4
Number of loan classes | loan_class					8
Number of loan pools | loan_pool					19
Number of loan pools with insignificant current balances | loan_pool					3
Number of loan pools with significant current balances | loan_pool					16
Number of econometric regression models used to estimate probability of default | model					7
Number of loss given default pools | loan_pool					9
Retained earnings	$ 292,561				$ 292,561			$ 1,652,248
Allowance for credit losses	442,537	$ 381,621		$ 172,413	442,537	$ 172,413	$ 181,973	$ 174,646	$ 169,898	$ 169,333
Goodwill impairment	$ 0	$ 0	$ 1,470,000	$ 0	$ 1,470,000	$ 0
CALIFORNIA
Business Acquisition [Line Items]
Retail branch locations | bank_branch					71
NORTH CAROLINA
Business Acquisition [Line Items]
Retail branch locations | bank_branch					1
COLORADO
Business Acquisition [Line Items]
Retail branch locations | bank_branch					1
Cumulative Effect, Period Of Adoption, Adjustment | Accounting Standards Update 2016-13 [Member]
Business Acquisition [Line Items]
Retained earnings							5,300
Allowance for credit losses							$ 7,300