Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	$ 435,597		$ 236,568
Beginning balance - Incurred Loss Model		$ 202,534	210,759	$ 207,457
Provision for loan losses - CECL	6,609		236,938
Provision for loan losses - incurred		12,539		25,426
Loans charged off	(26,661)	(11,707)	(61,148)	(36,709)
Recoveries of loans previously charged off	4,232	1,066	7,419	8,258
Ending balance - CECL	419,777		419,777
Ending balance - Incurred Loss Model	419,777	204,432	419,777	204,432
Provision Details [Abstract]
Change in provision due to changes in reasonable and supportable forecasts, primarily due to COVID-19 pandemic	(12,800)
Other changes to provision	14,500
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	32,919		25,137
Provision for off-balance sheet credit risk	(4,950)		2,832
Ending balance - CECL	27,969		27,969
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		1,903		1,790
Provision for off-balance sheet credit losses		(539)		(426)
Ending balance - Incurred Loss Model		1,364		1,364
Total provision for credit losses	0	12,000	229,092	25,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					$ 23,582,147	$ 21,570,036
Individually measured for impairment, recorded investment					221,153	180,951
Total					23,803,300	21,750,987
Related allowance [Abstract]
Collectively measured for impairment, related allowance					400,082	176,150
Individually measured for impairment, related allowance					19,695	17,414
Total	419,777	204,432	419,777	207,457	419,777	210,759
Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	310,422		151,868
Beginning balance - Incurred Loss Model		106,397	118,187	102,226
Provision for loan losses - CECL	2,108		190,984
Provision for loan losses - incurred		9,861		34,740
Loans charged off	(25,319)	(9,875)	(56,421)	(31,728)
Recoveries of loans previously charged off	3,066	260	3,846	1,405
Ending balance - CECL	290,277		290,277
Ending balance - Incurred Loss Model	290,277	106,643	290,277	106,643
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	14,582		11,578
Provision for off-balance sheet credit risk	(2,618)		386
Ending balance - CECL	11,964		11,964
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		1,742		1,655
Provision for off-balance sheet credit losses		(536)		(449)
Ending balance - Incurred Loss Model		1,206		1,206
Total provision for credit losses		9,325		34,291
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					13,395,753	13,916,234
Individually measured for impairment, recorded investment					169,953	115,416
Total					13,565,706	14,031,650
Related allowance [Abstract]
Collectively measured for impairment, related allowance					271,122	100,773
Individually measured for impairment, related allowance					19,155	17,414
Total	290,277	106,643	118,187	102,226	290,277	118,187
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	68,756		47,185
Beginning balance - Incurred Loss Model		54,188	51,805	60,026
Provision for loan losses - CECL	3,118		25,454
Provision for loan losses - incurred		102		(10,075)
Loans charged off	(413)	0	(1,300)	(118)
Recoveries of loans previously charged off	114	60	236	4,517
Ending balance - CECL	71,575		71,575
Ending balance - Incurred Loss Model	71,575	54,350	71,575	54,350
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	16,419		11,767
Provision for off-balance sheet credit risk	(2,426)		2,226
Ending balance - CECL	13,993		13,993
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		116		52
Provision for off-balance sheet credit losses		(3)		61
Ending balance - Incurred Loss Model		113		113
Total provision for credit losses		99		(10,014)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					4,680,748	4,406,157
Individually measured for impairment, recorded investment					12,952	27,626
Total					4,693,700	4,433,783
Related allowance [Abstract]
Collectively measured for impairment, related allowance					71,035	51,805
Individually measured for impairment, related allowance					540	0
Total	71,575	54,350	51,805	60,026	71,575	51,805
Paycheck Protection Program
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	0		0
Provision for loan losses - CECL	0		0
Loans charged off	0		0
Recoveries of loans previously charged off	0		0
Ending balance - CECL	0		0
Ending balance - Incurred Loss Model	0		0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	0		0
Provision for off-balance sheet credit risk	0		0
Ending balance - CECL	0		0
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					2,097,325
Individually measured for impairment, recorded investment					0
Total					2,097,325
Related allowance [Abstract]
Collectively measured for impairment, related allowance					0
Individually measured for impairment, related allowance					0
Total	0		0		0
Loans to individuals [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	56,419		37,515
Provision for loan losses - CECL	1,383		20,500
Loans charged off	(929)		(3,427)
Recoveries of loans previously charged off	1,052		3,337
Ending balance - CECL	57,925		57,925
Ending balance - Incurred Loss Model	57,925		57,925
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	1,918		1,792
Provision for off-balance sheet credit risk	94		220
Ending balance - CECL	2,012		2,012
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					3,408,321
Individually measured for impairment, recorded investment					38,248
Total					3,446,569	2,084,172
Related allowance [Abstract]
Collectively measured for impairment, related allowance					57,925
Individually measured for impairment, related allowance					0
Total	57,925		57,925		57,925
Loans to individuals [Member] | Residential mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - Incurred Loss Model		15,724	14,400	17,964
Provision for loan losses - incurred		(253)		(2,660)
Loans charged off		(56)		(192)
Recoveries of loans previously charged off		119		422
Ending balance - Incurred Loss Model		15,534		15,534
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		44		52
Provision for off-balance sheet credit losses		0		(8)
Ending balance - Incurred Loss Model		44		44
Total provision for credit losses		(253)		(2,668)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment						2,046,550
Individually measured for impairment, recorded investment						37,622
Total					1,849,144	2,084,172
Related allowance [Abstract]
Collectively measured for impairment, related allowance						14,400
Individually measured for impairment, related allowance						0
Total		15,534	14,400	15,534		14,400
Loans to individuals [Member] | Personal [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - Incurred Loss Model		9,388	9,172	9,473
Provision for loan losses - incurred		1,911		3,434
Loans charged off		(1,776)		(4,671)
Recoveries of loans previously charged off		627		1,914
Ending balance - Incurred Loss Model		10,150		10,150
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		1		31
Provision for off-balance sheet credit losses		0		(30)
Ending balance - Incurred Loss Model		1		1
Total provision for credit losses		1,911		3,404
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment						1,201,095
Individually measured for impairment, recorded investment						287
Total					$ 1,213,178	1,201,382
Related allowance [Abstract]
Collectively measured for impairment, related allowance						9,172
Individually measured for impairment, related allowance						0
Total		10,150	9,172	10,150		9,172
Specific Allowance [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - Incurred Loss Model			193,564
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment						21,570,036
Individually measured for impairment, recorded investment						180,951
Total						21,750,987
Related allowance [Abstract]
Collectively measured for impairment, related allowance						176,150
Individually measured for impairment, related allowance						17,414
Total			193,564			193,564
Nonspecific Allowance [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	0		0
Beginning balance - Incurred Loss Model		16,837	17,195	17,768
Provision for loan losses - CECL	0		0
Provision for loan losses - incurred		918		(13)
Loans charged off	0	0	0	0
Recoveries of loans previously charged off	0	0	0	0
Ending balance - CECL	0		0
Ending balance - Incurred Loss Model		17,755		17,755
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	0		0
Provision for off-balance sheet credit risk	0		0
Ending balance - CECL	$ 0		0
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		0		0
Provision for off-balance sheet credit losses		0		0
Ending balance - Incurred Loss Model		0		0
Total provision for credit losses		918		(13)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment						0
Individually measured for impairment, recorded investment						0
Total						0
Related allowance [Abstract]
Collectively measured for impairment, related allowance						0
Individually measured for impairment, related allowance						0
Total		$ 17,755	17,195	$ 17,768		$ 17,195
Previously Reported [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			210,759
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			1,585
Previously Reported [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			118,187
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			1,434
Previously Reported [Member] | Commercial real estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			51,805
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			107
Previously Reported [Member] | Paycheck Protection Program
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			0
Previously Reported [Member] | Loans to individuals [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			23,572
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			44
Previously Reported [Member] | Nonspecific Allowance [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			17,195
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			0
Restatement Adjustment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			25,809
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			23,552
Restatement Adjustment [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			33,681
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			10,144
Restatement Adjustment [Member] | Commercial real estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			(4,620)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			11,660
Restatement Adjustment [Member] | Paycheck Protection Program
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			0
Restatement Adjustment [Member] | Loans to individuals [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			13,943
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			1,748
Restatement Adjustment [Member] | Nonspecific Allowance [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL			(17,195)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL			$ 0