Fair Value Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 540,964	$ 495,574	$ 685,302
Available-for-sale securities	1,949,697	2,176,290	1,870,831
Trading account securities	1,068	497	1,036
Brokerage customer receivables	26,884	30,953	25,614
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	78,524	79,261	76,601
FDIC indemnification asset	60,298	85,672	170,696	208,160
Federal Home Loan Bank advances	387,672	417,762	414,032
Subordinated notes	0	0	15,000
Other borrowings	230,904	254,740	256,244
Junior subordinated debentures	249,493	249,493	249,493
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	342,738	263,864	213,201
Interest bearing deposits with banks	540,964	495,574	685,302
Available-for-sale securities	1,949,697	2,176,290	1,870,831
Trading account securities	1,068	497	1,036
Brokerage customer receivables	26,884	30,953	25,614
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	78,524	79,261	76,601
Mortgage loans held-for-sale, at fair value	215,231	332,485	370,570
Mortgage loans held-for-sale, at lower of cost or market	0	1,842	10,352
Total loans	13,445,638	13,243,033	12,418,973
Mortgage servicing rights	8,719	8,946	7,344
Nonqualified deferred compensation assets	7,783	7,222	6,545
Derivative assets	51,529	48,221	52,436
FDIC indemnification asset	60,298	85,672	170,696
Accrued interest receivable and other	169,580	163,732	156,825
Total financial assets	16,898,653	16,937,592	16,066,326
Non-maturity deposits	10,944,521	10,442,077	9,293,104
Deposits with stated maturities	4,184,524	4,226,712	4,669,653
Notes payable	182	364	31,911
Federal Home Loan Bank advances	387,672	417,762	414,032
Subordinated notes	0	0	15,000
Other borrowings	230,904	254,740	256,244
Junior subordinated debentures	249,493	249,493	249,493
Derivative liabilities	37,797	37,264	54,745
Interest Payable, Current	7,218	8,556	11,520
Total financial liabilities	16,042,311	15,636,968	14,995,702
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	342,738	263,864	213,201
Interest bearing deposits with banks	540,964	495,574	685,302
Available-for-sale securities	1,949,697	2,176,290	1,870,831
Trading account securities	1,068	497	1,036
Brokerage customer receivables	26,884	30,953	25,614
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	78,524	79,261	76,601
Mortgage loans held-for-sale, at fair value	215,231	332,485	370,570
Mortgage loans held-for-sale, at lower of cost or market	0	1,857	10,458
Total loans	14,078,788	13,867,255	13,125,643
Mortgage servicing rights	8,719	8,946	7,344
Nonqualified deferred compensation assets	7,783	7,222	6,545
Derivative assets	51,529	48,221	52,436
FDIC indemnification asset	60,298	85,672	170,696
Accrued interest receivable and other	169,580	163,732	156,825
Total financial assets	17,531,803	17,561,829	16,773,102
Non-maturity deposits	10,944,521	10,442,077	9,293,104
Deposits with stated maturities	4,197,918	4,242,172	4,701,049
Notes payable	182	364	31,911
Federal Home Loan Bank advances	393,145	422,750	425,103
Subordinated notes	0	0	15,000
Other borrowings	230,904	254,740	256,244
Junior subordinated debentures	250,578	250,672	250,470
Derivative liabilities	37,797	37,264	54,745
Interest Payable, Current	7,218	8,556	11,520
Total financial liabilities	$ 16,062,263	$ 15,658,595	$ 15,039,146