Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	98,287		98,287		106,201
Outstanding principal balance of residential mortgage loans serviced for others	$ 14,887,909,000		$ 14,887,909,000		$ 16,228,449,000
Weighted average interest rate	3.73%		3.73%		3.84%
Remaining term (in months)			278		280
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 132,915,000	$ 110,828,000	$ 101,172,000	$ 201,886,000	$ 201,886,000
Additions	7,937,000	8,465,000	17,767,000	13,906,000
Disposals	0	(10,801,000)	0	(10,801,000)
Change in fair value due to principal payments	(10,182,000)	(9,760,000)	(22,143,000)	(17,779,000)
Change in fair value due to market assumption changes	(13,041,000)	(761,000)	20,833,000	(89,241,000)
Ending balance	$ 117,629,000	$ 97,971,000	$ 117,629,000	$ 97,971,000	$ 101,172,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			8.87%		9.14%
Prepayment rate - based upon loan interest rate, original term and loan type, minimum			7.81%		9.41%
Prepayment rate - based upon loan interest rate, original term and loan type, maximum			19.08%		21.87%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)			$ 69		$ 69
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)			94		94
Loan servicing costs - annually per loan based upon loan type, delinquent, minimum (in dollars per loan)			150		150
Loan servicing costs - annually per loan based upon loan type, delinquent, maximum (in dollars per loan)			500		500
Loan servicing costs - annually per loan based upon loan type, foreclosure, minimum (in dollars per loan)			1,000		1,000
Loan servicing costs - annually per loan based upon loan type, foreclosure, maximum (in dollars per loan)			$ 4,000		$ 4,000
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)			0.95%		0.43%
Primary secondary mortgage rate spread	105		105		105
Delinquency rate			2.67%		3.54%