Fair Value of Assets and Liabilities (Summary of Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 2,164,560	$ 1,099,594
Available-for-sale securities	3,106,214	2,126,081
Held-to-maturity securities	1,134,400	1,067,439
Trading account securities	1,068	1,692
Equity securities with readily determinable fair value	50,840	34,717
FHLB and FRB stock, at cost	100,739	91,354
Brokerage customer receivables	16,573	12,609
Mortgage loans held-for-sale, at fair value	377,313	264,070
Accrued interest receivable and other	1,061,141	696,707
FHLB advances	674,870	426,326
Other borrowings	418,174	393,855
Subordinated notes	436,095	139,210
Junior subordinated debentures	253,566	253,566
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	286,476	392,200
Interest bearing deposits with banks	2,164,560	1,099,594
Available-for-sale securities	3,106,214	2,126,081
Held-to-maturity securities	1,134,400	1,067,439
Trading account securities	1,068	1,692
Equity securities with readily determinable fair value	50,840	34,717
FHLB and FRB stock, at cost	100,739	91,354
Brokerage customer receivables	16,573	12,609
Mortgage loans held-for-sale, at fair value	377,313	264,070
Loans held-for-investment, at fair value	132,718	93,857
Loans held-for-investment, at amortized cost	26,667,572	23,726,834
Nonqualified deferred compensation assets	14,213	11,282
Derivative assets	103,644	73,172
Accrued interest receivable and other	303,090	260,281
Total financial assets	34,459,420	29,255,182
Non-maturity deposits	24,483,867	20,833,837
Deposits with stated maturities	5,623,271	5,260,841
FHLB advances	674,870	426,326
Other borrowings	418,174	393,855
Subordinated notes	436,095	139,210
Junior subordinated debentures	253,566	253,566
Derivative liabilities	129,204	68,088
Accrued interest payable	19,940	16,025
Total financial liabilities	32,038,987	27,391,748
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	286,476	392,200
Interest bearing deposits with banks	2,164,560	1,099,594
Available-for-sale securities	3,106,214	2,126,081
Held-to-maturity securities	1,138,396	1,036,096
Trading account securities	1,068	1,692
Equity securities with readily determinable fair value	50,840	34,717
FHLB and FRB stock, at cost	100,739	91,354
Brokerage customer receivables	16,573	12,609
Mortgage loans held-for-sale, at fair value	377,313	264,070
Loans held-for-investment, at fair value	132,718	93,857
Loans held-for-investment, at amortized cost	26,659,903	23,780,739
Nonqualified deferred compensation assets	14,213	11,282
Derivative assets	103,644	73,172
Accrued interest receivable and other	303,090	260,281
Total financial assets	34,455,747	29,277,744
Non-maturity deposits	24,483,867	20,833,837
Deposits with stated maturities	5,635,475	5,283,063
FHLB advances	715,129	429,830
Other borrowings	418,174	393,855
Subordinated notes	458,796	138,345
Junior subordinated debentures	243,158	263,846
Derivative liabilities	129,204	68,088
Accrued interest payable	19,940	16,025
Total financial liabilities	$ 32,103,743	$ 27,426,889