Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Held-to-Maturity Estimated Fair Value	$ 513,273	$ 607,550
Carrying Amount
Financial assets:
Cash and cash equivalents	782,023	780,457
Investment securities available-for-sale	1,611,698	1,456,840
Held-to-Maturity Estimated Fair Value	512,770	600,665
Accrued interest receivable	29,852	27,729
Mortgage servicing rights	18,457	15,621
Net loans	5,402,330	5,169,379
Derivative Asset	2,749	953
Deferred Compensation Plan Assets	10,627	10,149
Total financial assets	8,370,506	8,061,793
Financial liabilities:
Total deposits, excluding time deposits	6,324,512	5,957,345
Time deposits	1,051,598	1,131,592
Securities sold under repurchase agreements	537,556	510,635
Other borrowed funds	6	2
Accrued interest payable	5,421	4,960
Long-term debt	27,970	27,885
Subordinated debentures held by subsidiary trusts	82,477	82,477
Derivative Liability	1,314	829
Deferred Compensation Liability, Current and Noncurrent	10,627	10,149
Total financial liabilities	8,041,481	7,725,874
Estimated Fair Value
Financial assets:
Cash and cash equivalents	782,023	780,457
Investment securities available-for-sale	1,611,698	1,456,840
Held-to-Maturity Estimated Fair Value	513,273	607,550
Accrued interest receivable	29,852	27,729
Mortgage servicing rights	35,656	31,011
Net loans	5,309,921	5,128,705
Derivative Asset	2,749	953
Deferred Compensation Plan Assets	10,627	10,149
Total financial assets	8,295,799	8,043,394
Financial liabilities:
Total deposits, excluding time deposits	6,324,512	5,975,345
Time deposits	1,044,670	1,137,289
Securities sold under repurchase agreements	537,556	510,635
Other borrowed funds	6	2
Accrued interest payable	5,421	4,960
Long-term debt	27,477	27,622
Subordinated debentures held by subsidiary trusts	73,554	74,969
Derivative Liability	1,314	829
Deferred Compensation Liability, Current and Noncurrent	10,627	10,149
Total financial liabilities	8,025,137	7,741,800
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	782,023	780,457
Investment securities available-for-sale	0	0
Held-to-Maturity Estimated Fair Value	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Net loans	0	0
Derivative Asset	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	782,023	780,457
Financial liabilities:
Total deposits, excluding time deposits	6,324,512	5,975,345
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	6,324,512	5,975,345
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	1,611,698	1,456,840
Held-to-Maturity Estimated Fair Value	513,273	607,550
Accrued interest receivable	29,852	27,729
Mortgage servicing rights	35,656	31,011
Net loans	5,270,577	5,107,830
Derivative Asset	2,749	953
Deferred Compensation Plan Assets	10,627	10,149
Total financial assets	7,474,432	7,242,062
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,044,670	1,137,289
Securities sold under repurchase agreements	537,556	510,635
Other borrowed funds	6	2
Accrued interest payable	5,421	4,960
Long-term debt	27,477	27,622
Subordinated debentures held by subsidiary trusts	73,554	74,969
Derivative Liability	1,314	829
Deferred Compensation Liability, Current and Noncurrent	10,627	10,149
Total financial liabilities	1,700,625	1,766,455
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	0	0
Held-to-Maturity Estimated Fair Value	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Net loans	39,344	20,875
Derivative Asset	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	39,344	20,875
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	$ 0	$ 0