Fair Value of Assets and Liabilities (Summary of Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 1,099,594	$ 1,063,242
Available-for-sale securities	2,126,081	1,803,666
Held-to-maturity securities	1,067,439	826,449
Trading account securities	1,692	995
Equity securities with readily determinable fair value	34,717	0
FHLB and FRB stock, at cost	91,354	89,989
Brokerage customer receivables	12,609	26,431
Mortgage loans held-for-sale	264,070	313,592
Mortgage servicing rights	75,183	33,676	$ 19,103	$ 9,092
Accrued interest receivable and other	696,707	567,374
FHLB advances	426,326	559,663
Other borrowings	393,855	266,123
Subordinated notes	139,210	139,088
Junior subordinated debentures	253,566	253,566
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	392,200	277,591
Interest bearing deposits with banks	1,099,594	1,063,242
Available-for-sale securities	2,126,081	1,803,666
Held-to-maturity securities	1,067,439	826,449
Trading account securities	1,692	995
Equity securities with readily determinable fair value	34,717	0
FHLB and FRB stock, at cost	91,354	89,989
Brokerage customer receivables	12,609	26,431
Mortgage loans held-for-sale	264,070	313,592
Loans held-for-investment, at fair value	93,857	33,717
Loans held-for-investment, at amortized cost	23,726,834	21,607,080
Mortgage servicing rights	75,183	33,676
Nonqualified deferred compensations assets	11,282	11,065
Derivative assets	73,172	52,069
Accrued interest receivable and other	260,281	227,649
Total financial assets	29,330,365	26,367,211
Non-maturity deposits	20,833,837	18,775,977
Deposits with stated maturities	5,260,841	4,407,370
FHLB advances	426,326	559,663
Other borrowings	393,855	266,123
Subordinated notes	139,210	139,088
Junior subordinated debentures	253,566	253,566
Derivative Liabilities	68,088	35,671
Accrued interest payable	16,025	8,030
Total financial liabilities	27,391,748	24,445,488
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	392,200	277,591
Interest bearing deposits with banks	1,099,594	1,063,242
Available-for-sale securities	2,126,081	1,803,666
Held-to-maturity securities	1,036,096	812,516
Trading account securities	1,692	995
Equity securities with readily determinable fair value	34,717	0
FHLB and FRB stock, at cost	91,354	89,989
Brokerage customer receivables	12,609	26,431
Mortgage loans held-for-sale	264,070	313,592
Loans held-for-investment, at fair value	93,857	33,717
Loans held-for-investment, at amortized cost	23,780,739	21,768,978
Mortgage servicing rights	75,183	33,676
Nonqualified deferred compensations assets	11,282	11,065
Derivative assets	73,172	52,069
Accrued interest receivable and other	260,281	227,649
Total financial assets	29,352,927	26,515,176
Non-maturity deposits	20,833,837	18,775,977
Deposits with stated maturities	5,283,063	4,350,004
FHLB advances	429,830	544,750
Other borrowings	393,855	266,123
Subordinated notes	138,345	144,266
Junior subordinated debentures	263,846	264,696
Derivative Liabilities	68,088	35,671
Accrued interest payable	16,025	8,030
Total financial liabilities	$ 27,426,889	$ 24,389,517