Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	$ 236,568
Beginning balance - Incurred Loss Model	210,759	$ 207,457
Provision for loan losses - CECL	95,964
Provision for loan losses - incurred		7,969
Loans charged off	(18,917)	(11,775)
Recoveries of loans previously charged off	1,696	1,689
Ending balance - CECL	315,311
Ending balance - Incurred Loss Model	315,311	205,340
Provision Details [Abstract]
Change in provision due to changes in reasonable and supportable forecasts, primarily due to COVID-19 pandemic	66,200
Other changes to provision	33,100
Provision change due to loan growth	7,500
Provision change due to changes in impairment, risk grading, and other portfolio changes	8,400
Provision changes due to net charge-offs	17,200
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	25,137
Provision for off-balance sheet credit risk	3,377
Ending balance - CECL	28,514
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		1,790
Provision for off-balance sheet credit losses		31
Ending balance - Incurred Loss Model		1,821
Total provision for credit losses	93,771	8,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			$ 22,300,798	$ 21,570,036
Individually measured for impairment, recorded investment			163,172	180,951
Total			22,463,970	21,750,987
Related allowance [Abstract]
Collectively measured for impairment, related allowance			305,427	176,150
Individually measured for impairment, related allowance			9,884	17,414
Total	210,759	205,340	315,311	210,759
Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	151,868
Beginning balance - Incurred Loss Model	118,187	102,226
Provision for loan losses - CECL	77,723
Provision for loan losses - incurred		11,108
Loans charged off	(16,615)	(10,468)
Recoveries of loans previously charged off	462	711
Ending balance - CECL	213,438
Ending balance - Incurred Loss Model	213,438	103,577
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	11,578
Provision for off-balance sheet credit risk	2,462
Ending balance - CECL	14,040
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		1,655
Provision for off-balance sheet credit losses		70
Ending balance - Incurred Loss Model		1,725
Total provision for credit losses		11,178
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			14,677,351	13,916,234
Individually measured for impairment, recorded investment			118,624	115,416
Total			14,795,975	14,031,650
Related allowance [Abstract]
Collectively measured for impairment, related allowance			203,554	100,773
Individually measured for impairment, related allowance			9,884	17,414
Total	118,187	103,577	213,438	118,187
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	47,185
Beginning balance - Incurred Loss Model	51,805	60,026
Provision for loan losses - CECL	5,115
Provision for loan losses - incurred		(2,004)
Loans charged off	(886)	0
Recoveries of loans previously charged off	47	112
Ending balance - CECL	51,461
Ending balance - Incurred Loss Model	51,461	58,134
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	11,767
Provision for off-balance sheet credit risk	808
Ending balance - CECL	12,575
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		52
Provision for off-balance sheet credit losses		(4)
Ending balance - Incurred Loss Model		48
Total provision for credit losses		(2,008)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			4,441,540	4,406,157
Individually measured for impairment, recorded investment			8,545	27,626
Total			4,450,085	4,433,783
Related allowance [Abstract]
Collectively measured for impairment, related allowance			51,461	51,805
Individually measured for impairment, related allowance			0	0
Total	51,805	58,134	51,461	51,805
Loans to individuals [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - CECL	37,515
Provision for loan losses - CECL	13,126
Loans charged off	(1,416)
Recoveries of loans previously charged off	1,187
Ending balance - CECL	50,412
Ending balance - Incurred Loss Model	50,412
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	1,792
Provision for off-balance sheet credit risk	107
Ending balance - CECL	1,899
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment			3,181,907
Individually measured for impairment, recorded investment			36,003
Total			3,217,910	2,084,172
Related allowance [Abstract]
Collectively measured for impairment, related allowance			50,412
Individually measured for impairment, related allowance			0
Total	50,412		50,412
Loans to individuals [Member] | Residential mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - Incurred Loss Model	14,400	17,964
Provision for loan losses - incurred		(2,408)
Loans charged off		(42)
Recoveries of loans previously charged off		154
Ending balance - Incurred Loss Model		15,668
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		52
Provision for off-balance sheet credit losses		(5)
Ending balance - Incurred Loss Model		47
Total provision for credit losses		(2,413)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				2,046,550
Individually measured for impairment, recorded investment				37,622
Total			1,844,555	2,084,172
Related allowance [Abstract]
Collectively measured for impairment, related allowance				14,400
Individually measured for impairment, related allowance				0
Total	14,400	15,668		14,400
Loans to individuals [Member] | Personal [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance - Incurred Loss Model	9,172	9,473
Provision for loan losses - incurred		(137)
Loans charged off		(1,265)
Recoveries of loans previously charged off		712
Ending balance - Incurred Loss Model		8,783
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		31
Provision for off-balance sheet credit losses		(30)
Ending balance - Incurred Loss Model		1
Total provision for credit losses		(167)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				1,201,095
Individually measured for impairment, recorded investment				287
Total			$ 1,175,466	1,201,382
Related allowance [Abstract]
Collectively measured for impairment, related allowance				9,172
Individually measured for impairment, related allowance				0
Total	9,172	8,783		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
Beginning balance - Incurred Loss Model	17,195	17,768
Provision for loan losses - CECL	0
Provision for loan losses - incurred		1,410
Loans charged off	0	0
Recoveries of loans previously charged off	0	0
Ending balance - CECL	0
Ending balance - Incurred Loss Model		19,178
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance - CECL	0
Provision for off-balance sheet credit risk	0
Ending balance - CECL	0
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred Loss Model		0
Provision for off-balance sheet credit losses		0
Ending balance - Incurred Loss Model		0
Total provision for credit losses		1,410
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	17,195	$ 19,178		$ 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] | 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] | 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