Accounting Standards Updates and Recently Adopted Standards (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in ACL		$ 146,176	$ 115,769	$ 65,547	$ 65,972	$ 65,595	$ 64,613
Increase in ACL for loans		134,256		62,089	62,514		61,203
Increase in ACL for unfunded commitments		11,920	12,100	3,458	3,458	3,391	3,410
Reduction in equity		(1,967,255)	(1,771,645)	(1,635,692)	(1,605,425)	(1,566,334)	(1,457,554)
Adoption of CECL
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in ACL				8,751
Increase in ACL for loans				6,880
Increase in ACL for unfunded commitments				1,871
Reduction in equity				3,529			549
Adoption of CECL | ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in ACL				8,750
Increase in ACL for loans				6,880
Increase in ACL for unfunded commitments				1,870
Increase reclassified from amortized cost basis of PCD financial assets previously classified as PCI	$ 3,590
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction in equity		$ (94,938)	$ (64,990)	(40,152)	$ (5,594)	$ 29,116	90,419
Retained earnings | Adoption of CECL
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction in equity				3,529			$ 549
Retained earnings | Adoption of CECL | ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction in equity				$ 3,530