Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	$ 236,568,000
Provision for loan losses - CECL	222,460,000
Loans charged off	(79,399,000)	$ (50,977,000)	$ (43,583,000)
Recoveries of loans previously charged off	9,011,000	10,074,000	10,414,000
Beginning balance, Incurred Loss Model	210,759,000	207,457,000	230,682,000
Provision for loan losses		44,205,000	9,944,000
Ending Balance - CECL	388,640,000	236,568,000
Ending balance, Incurred Loss Model	388,640,000	210,759,000	207,457,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	25,137,000
Provision for off-balance sheet credit risk	11,784,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	36,921,000	25,137,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	1,585,000	1,790,000	3,734,000
Provision for off-balance sheet credit losses		(205,000)	(1,944,000)
Ending balance - Incurred loss model		1,585,000	1,790,000
Total provision for credit losses	222,592,000	44,000,000	8,000,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				$ 22,772,827,000	$ 21,570,036,000
Individually measured for impairment, recorded investment				234,693,000	180,951,000
Total				23,007,520,000	21,750,987,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance				366,199,000	176,150,000
Individually measured for impairment, related allowance				22,441,000	17,414,000
Total measured for impairment, related allowance	210,759,000	210,759,000	207,457,000	388,640,000	210,759,000
Provision Details [Abstract]
Change in provision due to changes in reasonable and supportable forecasts, primarily due to COVID-19 pandemic [Line Items]	99,100,000
Other changes to provision	135,200,000
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	151,868,000
Provision for loan losses - CECL	171,800,000
Loans charged off	(73,370,000)	(43,185,000)	(37,880,000)
Recoveries of loans previously charged off	4,636,000	2,021,000	3,316,000
Beginning balance, Incurred Loss Model	118,187,000	102,226,000	124,269,000
Provision for loan losses		57,125,000	12,521,000
Ending Balance - CECL	254,934,000	151,868,000
Ending balance, Incurred Loss Model	254,934,000	118,187,000	102,226,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	11,578,000
Provision for off-balance sheet credit risk	2,844,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	14,422,000	11,578,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	1,434,000	1,655,000	3,644,000
Provision for off-balance sheet credit losses		(221,000)	(1,989,000)
Ending balance - Incurred loss model		1,434,000	1,655,000
Total provision for credit losses		56,904,000	10,532,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				12,910,376,000	13,916,234,000
Individually measured for impairment, recorded investment				167,159,000	115,416,000
Total				13,077,535,000	14,031,650,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance				235,882,000	100,773,000
Individually measured for impairment, related allowance				19,052,000	17,414,000
Total measured for impairment, related allowance	118,187,000	118,187,000	124,269,000	254,934,000	118,187,000
Commercial real estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	47,185,000
Provision for loan losses - CECL	40,407,000
Loans charged off	(1,300,000)	(1,161,000)	0
Recoveries of loans previously charged off	266,000	4,986,000	3,552,000
Beginning balance, Incurred Loss Model	51,805,000	60,026,000	56,621,000
Provision for loan losses		(12,046,000)	(147,000)
Ending Balance - CECL	86,558,000	47,185,000
Ending balance, Incurred Loss Model	86,558,000	51,805,000	60,026,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	11,767,000
Provision for off-balance sheet credit risk	8,804,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	20,571,000	11,767,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	107,000	52,000	45,000
Provision for off-balance sheet credit losses		55,000	7,000
Ending balance - Incurred loss model		107,000	52,000
Total provision for credit losses		(11,991,000)	(140,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				4,671,292,000	4,406,157,000
Individually measured for impairment, recorded investment				27,246,000	27,626,000
Total				4,698,538,000	4,433,783,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance				83,169,000	51,805,000
Individually measured for impairment, related allowance				3,389,000	0
Total measured for impairment, related allowance	51,805,000	51,805,000	56,621,000	86,558,000	51,805,000
Paycheck Protection Program
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	0
Provision for loan losses - CECL	0
Loans charged off	0
Recoveries of loans previously charged off	0
Ending Balance - CECL	0	0
Ending balance, Incurred Loss Model	0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	0
Provision for off-balance sheet credit risk	0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	0	0
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				1,682,310,000
Individually measured for impairment, recorded investment				0
Total				1,682,310,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance				0
Individually measured for impairment, related allowance				0
Total measured for impairment, related allowance	0			0
Loans to individuals [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	37,515,000
Provision for loan losses - CECL	10,253,000
Loans charged off	(4,729,000)
Recoveries of loans previously charged off	4,109,000
Ending Balance - CECL	47,148,000	37,515,000
Ending balance, Incurred Loss Model	47,148,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	1,792,000
Provision for off-balance sheet credit risk	136,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	1,928,000	1,792,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				3,508,849,000
Individually measured for impairment, recorded investment				40,288,000
Total				3,549,137,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance				47,148,000
Individually measured for impairment, related allowance				0
Total measured for impairment, related allowance	47,148,000			47,148,000
Loans to individuals [Member] | Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Loans charged off		(288,000)	(378,000)
Recoveries of loans previously charged off		562,000	1,047,000
Beginning balance, Incurred Loss Model	14,400,000	17,964,000	18,451,000
Provision for loan losses		(3,838,000)	(1,156,000)
Ending balance, Incurred Loss Model		14,400,000	17,964,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	44,000	52,000	43,000
Provision for off-balance sheet credit losses		(8,000)	9,000
Ending balance - Incurred loss model		44,000	52,000
Total provision for credit losses		(3,846,000)	(1,147,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					2,046,550,000
Individually measured for impairment, recorded investment					37,622,000
Total					2,084,172,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance					14,400,000
Individually measured for impairment, related allowance					0
Total measured for impairment, related allowance	14,400,000	14,400,000	17,964,000		14,400,000
Loans to individuals [Member] | Personal [Member]
Allowance for loan losses [Roll Forward]
Loans charged off		(6,343,000)	(5,325,000)
Recoveries of loans previously charged off		2,505,000	2,499,000
Beginning balance, Incurred Loss Model	9,172,000	9,473,000	9,124,000
Provision for loan losses		3,537,000	3,175,000
Ending balance, Incurred Loss Model		9,172,000	9,473,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	0	31,000	2,000
Provision for off-balance sheet credit losses		(31,000)	29,000
Ending balance - Incurred loss model		0	31,000
Total provision for credit losses		3,506,000	3,204,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					1,201,095,000
Individually measured for impairment, recorded investment					287,000
Total				$ 1,277,447,000	1,201,382,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance					9,172,000
Individually measured for impairment, related allowance					0
Total measured for impairment, related allowance	9,172,000	9,172,000	9,124,000		9,172,000
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	0
Provision for loan losses - CECL	0
Loans charged off	0	0	0
Recoveries of loans previously charged off	0	0	0
Beginning balance, Incurred Loss Model	17,195,000	17,768,000	22,217,000
Provision for loan losses		(573,000)	(4,449,000)
Ending Balance - CECL	0	0
Ending balance, Incurred Loss Model		17,195,000	17,768,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	0
Provision for off-balance sheet credit risk	0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL	0	0
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance - Incurred loss model	0	0	0
Provision for off-balance sheet credit losses		0	0
Ending balance - Incurred loss model		0	0
Total provision for credit losses		(573,000)	(4,449,000)
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 measured for impairment, related allowance	17,195,000	17,195,000	$ 22,217,000		17,195,000
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance, Incurred Loss Model	193,564,000
Ending balance, Incurred Loss Model		193,564,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					21,570,036,000
Individually measured for impairment, recorded investment					180,951,000
Total					21,750,987,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance					176,150,000
Individually measured for impairment, related allowance					17,414,000
Total measured for impairment, related allowance	193,564,000	193,564,000			$ 193,564,000
Transition Adjustment [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	25,809,000
Ending Balance - CECL		25,809,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	23,552,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		23,552,000
Transition Adjustment [Member] | Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	33,681,000
Ending Balance - CECL		33,681,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	10,144,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		10,144,000
Transition Adjustment [Member] | Commercial real estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	(4,620,000)
Ending Balance - CECL		(4,620,000)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	11,660,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		11,660,000
Transition Adjustment [Member] | Paycheck Protection Program
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	0
Ending Balance - CECL		0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		0
Transition Adjustment [Member] | Loans to individuals [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	13,943,000
Ending Balance - CECL		13,943,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	1,748,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		1,748,000
Transition Adjustment [Member] | Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	(17,195,000)
Ending Balance - CECL		(17,195,000)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		0
Previously Reported [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	210,759,000
Ending Balance - CECL		210,759,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	1,585,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		1,585,000
Previously Reported [Member] | Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	118,187,000
Ending Balance - CECL		118,187,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	1,434,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		1,434,000
Previously Reported [Member] | Commercial real estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	51,805,000
Ending Balance - CECL		51,805,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	107,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		107,000
Previously Reported [Member] | Paycheck Protection Program
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	0
Ending Balance - CECL		0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		0
Previously Reported [Member] | Loans to individuals [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	23,572,000
Ending Balance - CECL		23,572,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	44,000
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		44,000
Previously Reported [Member] | Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance - CECL	17,195,000
Ending Balance - CECL		17,195,000
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Off-Balance Sheet, Credit Loss, Liability, Beginning Balance - CECL	$ 0
Off-Balance Sheet, Credit Loss, Liability, Ending Balance - CECL		$ 0