New Authoritative Accounting Guidance (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Forecast period	2 years
Historical loss experience period	1 year
Allowance for loan losses	$ 325,032	$ 161,759	$ 309,614		$ 161,853	$ 155,105		$ 151,859
Allowance for unfunded credit commitments	10,296	2,845
Allowance for credit losses	1,481
Stockholders' equity	(4,533,763)	(4,384,188)	(4,474,488)	$ (4,420,998)	(3,558,075)	(3,504,118)	$ (3,444,879)	(3,350,454)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	$ (553,826)	(443,559)	$ (499,511)	$ (452,424)	$ (454,020)	$ (412,190)	$ (375,983)	$ (299,642)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		100,400
Allowance for loan losses		92,531
Allowance for unfunded credit commitments		7,100
Allowance for credit losses		793
PCD loans related reserves		61,600
Non-credit discount		97,700
Stockholders' equity		28,187
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity		28,187
Cumulative Effect, Period of Adoption, Adjustment | Non-PCD Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan losses		$ 38,800