Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial assets:
Investment securities held-to-maturity	$ 607,550	$ 584,533
Carrying Amount
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	600,665	575,186
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	15,621	14,038
Net loans	5,169,379	4,823,243
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	8,061,793	7,960,497
Financial liabilities:
Total deposits, excluding time deposits	5,957,345	5,767,992
Time deposits	1,131,592	1,238,220
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,885	38,067
Subordinated debentures held by subsidiary trusts	82,477	82,477
Derivative Liability	829	829
Deferred Compensation Liability, Current and Noncurrent	10,149	10,149
Total financial liabilities	7,725,874	7,645,826
Estimated Fair Value
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	607,550	584,533
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	31,011	21,434
Net loans	5,128,705	4,800,725
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	8,043,394	7,954,722
Financial liabilities:
Total deposits, excluding time deposits	5,975,345	5,767,992
Time deposits	1,137,289	1,244,324
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,622	37,781
Subordinated debentures held by subsidiary trusts	74,969	75,734
Derivative Liability	829	59
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Total financial liabilities	7,741,800	7,644,294
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	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	780,457	798,670
Financial liabilities:
Total deposits, excluding time deposits	5,975,345	5,767,992
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	5,975,345	5,767,992
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	607,550	584,533
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	31,011	21,434
Net loans	5,107,830	4,770,231
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	7,242,062	7,125,558
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,137,289	1,244,324
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,622	37,781
Subordinated debentures held by subsidiary trusts	74,969	75,734
Derivative Liability	829	59
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Total financial liabilities	1,766,455	1,876,302
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Net loans	20,875	30,494
Derivative Asset	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	20,875	30,494
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