Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financial assets:
Investment securities held-to-maturity	$ 553,323	$ 584,533
Carrying Amount
Financial assets:
Cash and cash equivalents	506,434	798,670
Investment securities available-for-sale	1,592,743	1,711,924
Investment securities held-to-maturity	546,690	575,186
Accrued interest receivable	29,008	27,063
Mortgage servicing rights	14,654	14,038
Net loans	5,027,394	4,823,243
Total financial assets	7,716,923	7,950,124
Financial liabilities:
Total deposits, excluding time deposits	5,655,166	5,767,992
Time deposits	1,149,235	1,238,220
Securities sold under repurchase agreements	469,145	502,250
Other borrowed funds	3	9
Accrued interest payable	5,366	5,833
Long-term debt	43,068	38,067
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total financial liabilities	7,404,460	7,634,848
Estimated Fair Value
Financial assets:
Cash and cash equivalents	506,434	798,670
Investment securities available-for-sale	1,592,743	1,711,924
Investment securities held-to-maturity	553,323	584,533
Accrued interest receivable	29,008	27,063
Mortgage servicing rights	28,320	21,434
Net loans	5,000,935	4,800,725
Total financial assets	7,710,763	7,944,349
Financial liabilities:
Total deposits, excluding time deposits	5,655,166	5,767,992
Time deposits	1,153,809	1,244,324
Securities sold under repurchase agreements	469,145	502,250
Other borrowed funds	3	9
Accrued interest payable	5,366	5,833
Long-term debt	41,584	37,781
Subordinated debentures held by subsidiary trusts	76,393	75,734
Total financial liabilities	7,401,466	7,633,923
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	506,434	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
Total financial assets	506,434	798,670
Financial liabilities:
Total deposits, excluding time deposits	5,655,166	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
Total financial liabilities	5,655,166	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	1,592,743	1,711,924
Investment securities held-to-maturity	553,323	584,533
Accrued interest receivable	29,008	27,063
Mortgage servicing rights	28,320	21,434
Net loans	4,950,804	4,770,231
Total financial assets	7,154,198	7,115,185
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,153,809	1,244,324
Securities sold under repurchase agreements	469,145	502,250
Other borrowed funds	3	9
Accrued interest payable	5,366	5,833
Long-term debt	41,584	37,781
Subordinated debentures held by subsidiary trusts	76,393	75,734
Total financial liabilities	1,746,300	1,865,931
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	50,131	30,494
Total financial assets	50,131	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
Total financial liabilities	$ 0	$ 0