Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financial assets:
Investment securities held-to-maturity	$ 535,145	$ 513,273
Carrying Amount
Financial assets:
Cash and cash equivalents	919,775	782,023
Investment securities available-for-sale	2,080,194	1,611,698
Investment securities held-to-maturity	529,442	512,770
Accrued interest receivable	35,830	29,852
Mortgage servicing rights	23,715	18,457
Mortgages Held-for-sale, Fair Value Disclosure	30,383	61,794
Loans Receivable, Fair Value Disclosure	7,449,889	5,340,536
Derivative Asset	10,599	2,749
Deferred compensation asset at fair value amount	11,598	10,627
Total financial assets	11,091,425	8,370,506
Financial liabilities:
Total deposits, excluding time deposits	8,817,211	6,324,512
Time deposits	1,202,789	1,051,598
Securities sold under repurchase agreements	579,772	537,556
Other borrowed funds	15,019	6
Accrued interest payable	8,917	5,421
Long-term debt	28,017	27,970
Subordinated debentures held by subsidiary trusts	82,477	82,477
Derivative Liability	9,797	1,314
Deferred compensation plan liabilities at fair value amount	11,598	10,627
Total financial liabilities	10,755,597	8,041,481
Estimated Fair Value
Financial assets:
Cash and cash equivalents	919,775	782,023
Investment securities available-for-sale	2,080,194	1,611,698
Investment securities held-to-maturity	535,145	513,273
Accrued interest receivable	35,830	29,852
Mortgage servicing rights	34,580	35,656
Mortgages Held-for-sale, Fair Value Disclosure	30,383	61,794
Loans Receivable, Fair Value Disclosure	7,325,012	5,248,127
Derivative Asset	10,599	2,749
Deferred compensation asset at fair value amount	11,598	10,627
Total financial assets	10,983,116	8,295,799
Financial liabilities:
Total deposits, excluding time deposits	8,817,211	6,324,512
Time deposits	1,195,454	1,044,670
Securities sold under repurchase agreements	579,772	537,556
Other borrowed funds	15,019	6
Accrued interest payable	8,917	5,421
Long-term debt	28,240	27,477
Subordinated debentures held by subsidiary trusts	91,519	73,554
Derivative Liability	9,797	1,314
Deferred compensation plan liabilities at fair value amount	11,598	10,627
Total financial liabilities	10,757,527	8,025,137
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	919,775	782,023
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Loans Receivable, Fair Value Disclosure	0	0
Derivative Asset	0	0
Deferred compensation asset at fair value amount	0	0
Total financial assets	919,775	782,023
Financial liabilities:
Total deposits, excluding time deposits	8,817,211	6,324,512
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 plan liabilities at fair value amount	0	0
Total financial liabilities	8,817,211	6,324,512
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	2,080,194	1,611,698
Investment securities held-to-maturity	535,145	513,273
Accrued interest receivable	35,830	29,852
Mortgage servicing rights	34,580	35,656
Mortgages Held-for-sale, Fair Value Disclosure	30,383	61,794
Loans Receivable, Fair Value Disclosure	7,290,037	5,208,783
Derivative Asset	10,599	2,749
Deferred compensation asset at fair value amount	11,598	10,627
Total financial assets	10,028,366	7,474,432
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,195,454	1,044,670
Securities sold under repurchase agreements	579,772	537,556
Other borrowed funds	15,019	6
Accrued interest payable	8,917	5,421
Long-term debt	28,240	27,477
Subordinated debentures held by subsidiary trusts	91,519	73,554
Derivative Liability	9,797	1,314
Deferred compensation plan liabilities at fair value amount	11,598	10,627
Total financial liabilities	1,940,316	1,700,625
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
Mortgages Held-for-sale, Fair Value Disclosure	0
Loans Receivable, Fair Value Disclosure	34,975	39,344
Derivative Asset	0	0
Deferred compensation asset at fair value amount	0	0
Total financial assets	34,975	39,344
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 plan liabilities at fair value amount	0	0
Total financial liabilities	$ 0	$ 0