Fair Value Measurement and Fair Value of Financial Instruments (Carrying and Fair Values Estimates per the Fair Value Hierarchy of Financial Instruments on a nonrecurring basis) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Financial assets:
Cash and cash equivalents	$ 4,017,971,000	$ 3,261,149,000
Interest-bearing deposits with banks	809,728,000	196,161,000
Resell agreements	1,460,000,000	860,000,000
Restricted equity securities, at cost	83,046,000	78,580,000
Loans held-for-investment, net	37,770,972,000	34,420,252,000
Financial liabilities:
Time deposits	9,000,349,000
Federal Home Loan Bank (“FHLB”) advances	652,612,000	745,915,000
Repurchase agreements	300,000,000	200,000,000
Gross repurchase agreements	300,000,000	450,000,000
Carrying amount of repurchase agreements eligible for netting against resale agreements	0	250,000,000
Carrying Amount
Financial assets:
Cash and cash equivalents	4,017,971,000	3,261,149,000
Interest-bearing deposits with banks	809,728,000	196,161,000
Resell agreements	1,460,000,000	860,000,000
Restricted equity securities, at cost	83,046,000	78,580,000
Loans held-for-sale	1,788,000	434,000
Loans held-for-investment, net	37,770,972,000	34,420,252,000
Mortgage servicing rights	5,522,000	6,068,000
Accrued interest receivable	150,140,000	144,599,000
Financial liabilities:
Demand, checking, savings and money market deposits	35,862,403,000	27,109,951,000
Time deposits	9,000,349,000	10,214,308,000
Short-term borrowings	21,009,000	28,669,000
Federal Home Loan Bank (“FHLB”) advances	652,612,000	745,915,000
Repurchase agreements	300,000,000	200,000,000
Long-term debt	147,376,000	147,101,000
Accrued interest payable	11,956,000	27,246,000
Estimated Fair Value
Financial assets:
Cash and cash equivalents	4,017,971,000	3,261,149,000
Interest-bearing deposits with banks	809,728,000	196,161,000
Resell agreements	1,464,635,000	856,025,000
Restricted equity securities, at cost	83,046,000	78,580,000
Loans held-for-sale	1,788,000	434,000
Loans held-for-investment, net	37,803,940,000	35,021,300,000
Mortgage servicing rights	8,435,000	8,199,000
Accrued interest receivable	150,140,000	144,599,000
Financial liabilities:
Demand, checking, savings and money market deposits	35,862,403,000	27,109,951,000
Time deposits	9,016,884,000	10,208,895,000
Short-term borrowings	21,009,000	28,669,000
Federal Home Loan Bank (“FHLB”) advances	659,631,000	755,371,000
Repurchase agreements	317,850,000	232,597,000
Long-term debt	150,131,000	152,641,000
Accrued interest payable	11,956,000	27,246,000
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	4,017,971,000	3,261,149,000
Interest-bearing deposits with banks	0	0
Resell agreements	0	0
Restricted equity securities, at cost	0	0
Loans held-for-sale	0	0
Loans held-for-investment, net	0	0
Mortgage servicing rights	0	0
Accrued interest receivable	0	0
Financial liabilities:
Demand, checking, savings and money market deposits	0	0
Time deposits	0	0
Short-term borrowings	0	0
Federal Home Loan Bank (“FHLB”) advances	0	0
Repurchase agreements	0	0
Long-term debt	0	0
Accrued interest payable	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Interest-bearing deposits with banks	809,728,000	196,161,000
Resell agreements	1,464,635,000	856,025,000
Restricted equity securities, at cost	83,046,000	78,580,000
Loans held-for-sale	1,788,000	434,000
Loans held-for-investment, net	0	0
Mortgage servicing rights	0	0
Accrued interest receivable	150,140,000	144,599,000
Financial liabilities:
Demand, checking, savings and money market deposits	35,862,403,000	27,109,951,000
Time deposits	9,016,884,000	10,208,895,000
Short-term borrowings	21,009,000	28,669,000
Federal Home Loan Bank (“FHLB”) advances	659,631,000	755,371,000
Repurchase agreements	317,850,000	232,597,000
Long-term debt	150,131,000	152,641,000
Accrued interest payable	11,956,000	27,246,000
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Interest-bearing deposits with banks	0	0
Resell agreements	0	0
Restricted equity securities, at cost	0	0
Loans held-for-sale	0	0
Loans held-for-investment, net	37,803,940,000	35,021,300,000
Mortgage servicing rights	8,435,000	8,199,000
Accrued interest receivable	0	0
Financial liabilities:
Demand, checking, savings and money market deposits	0	0
Time deposits	0	0
Short-term borrowings	0	0
Federal Home Loan Bank (“FHLB”) advances	0	0
Repurchase agreements	0	0
Long-term debt	0	0
Accrued interest payable	$ 0	$ 0