Recent Accounting and Regulatory Pronouncements - Impact of ASU (Details) - USD ($)		Jan. 01, 2020		Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Assets:
Securities available for sale, at fair value (cost of $3,498,087 and allowance for credit losses of $0 for September 30, 2020)				$ 3,561,929,000		$ 1,956,047,000	$ 1,813,134,000
Investment Securities - Held to Maturity				0
Non - Acquired Loans						11,375,104,000	11,290,147,000
Allowance for credit losses				(440,159,000)	$ (434,608,000)	(56,927,000)	(60,255,000)	$ (58,213,000)	$ (55,798,000)
Deferred tax assets				107,500,000		31,316,000	27,844,000
Accrued Interest Receivable - Loans				97,800,000
Liabilities:
Reserve for Loan Losses - Unfunded Commitments				440,159,000		56,927,000	54,937,000
Equity:
Retained Earnings (Accumulated Deficit)				604,564,000		679,895,000	646,325,000
Credit Discount on Acquired Credit Impaired Loans		$ 3,408,000
Financing Receivable, Allowance for Credit Losses				440,159,000	434,608,000	56,927,000	$ 60,255,000	$ 58,213,000	$ 55,798,000
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent		22.00%
Non-acquired loans
Assets:
Allowance for credit losses		$ (34,049,000)
Equity:
Financing Receivable, Allowance for Credit Losses		34,049,000
Acquired loans
Assets:
Allowance for credit losses		(16,981,000)
Equity:
Financing Receivable, Allowance for Credit Losses		16,981,000
Purchased Credit Deteriorated Loans [Member]
Assets:
Allowance for credit losses		(3,408,000)
Equity:
Financing Receivable, Allowance for Credit Losses		3,408,000
ASU 2016-13
Assets:
Acquired Loans	[1]	1,723,000
Allowance for credit losses	[2]	(54,438,000)
Deferred tax assets	[3]	12,639,000
Accrued Interest Receivable - Loans	[1]	1,677,000
Liabilities:
Reserve for Loan Losses - Unfunded Commitments	[4]	6,421,000
Equity:
Retained Earnings (Accumulated Deficit)		(44,820,000)	[5]			44,800,000
Financing Receivable, Allowance for Credit Losses	[2]	54,438,000
As previously recorded by acquiree | ASU 2016-13
Assets:
Securities available for sale, at fair value (cost of $3,498,087 and allowance for credit losses of $0 for September 30, 2020)		1,956,047,000
Non - Acquired Loans		9,252,831,000
Acquired Loans		2,118,940,000
Allowance for credit losses		(111,365,000)
Deferred tax assets		43,955,000
Accrued Interest Receivable - Loans		30,009,000
Liabilities:
Reserve for Loan Losses - Unfunded Commitments		6,756,000
Equity:
Retained Earnings (Accumulated Deficit)		635,075,000
Financing Receivable, Allowance for Credit Losses		111,365,000
Adjustments
Assets:
Allowance for credit losses					(433,066,000)	(111,365,000)
Equity:
Financing Receivable, Allowance for Credit Losses					$ 433,066,000	111,365,000
Adjustments | ASU 2016-13
Assets:
Securities available for sale, at fair value (cost of $3,498,087 and allowance for credit losses of $0 for September 30, 2020)		1,956,047,000
Non - Acquired Loans		9,252,831,000
Acquired Loans		2,117,209,000
Allowance for credit losses		(56,927,000)		(109,442,000)		(51,030,000)
Deferred tax assets		31,316,000
Accrued Interest Receivable - Loans		28,332,000
Liabilities:
Reserve for Loan Losses - Unfunded Commitments		335,000
Equity:
Retained Earnings (Accumulated Deficit)		679,895,000
Financing Receivable, Allowance for Credit Losses		$ 56,927,000		$ 109,442,000		$ 51,030,000

[1] Accrued interest receivable from acquired credit impaired loans of $1,677 was reclassified to other assets and was offset by the reclass of the grossed up credit discount on acquired credit impaired loans of $3,408 that was moved to the ACL for the purchased credit deteriorated loans.

[2] This is the calculated adjustment to the ACL related to the adoption of ASC 326. Additional reserve related to non-acquired loans was $34,049, to acquired loans was $16,981 and to purchased credit deteriorated loans was $3,408.

[3] This is the effect of deferred tax assets related to the adjustment to the ACL from the adoption of ASC 326 using a 22% tax rate.

[4] This is the adjustment to the reserve for unfunded commitments related to the adoption of ASC 326.

[5] This is the net adjustment to retained earnings related to the adoption of ASC 326.