Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 168,981	$ 153,691
Current	15,809,143	15,549,623
Total loans	15,978,124	15,703,314	$ 13,924,386
Recorded investment > 90 days and still accruing	9,226	7,653
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	82,017	79,027
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,126	12,101
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	72,838	62,563
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	168,528	153,075
Current	15,398,760	15,105,512
Total loans	15,567,288	15,258,587	12,920,530
Recorded investment > 90 days and still accruing	9,226	7,653
Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	82,017	79,012
Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,126	12,025
Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	72,385	62,038
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	453	616
Current	211,167	240,814
Total loans	211,620	241,430	765,324
Acquired Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		15
Acquired Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		76
Acquired Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	453	525
FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	199,216	203,297
Total loans	199,216	203,297	238,532
Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	24,817	24,365
Current	1,070,597	1,127,585
Total loans	1,095,414	1,151,950	1,113,510
Recorded investment > 90 days and still accruing	3,610	1,230
Construction and Land Development [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,007	19,886
Construction and Land Development [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	126	436
Construction and Land Development [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,684	4,043
Construction and Land Development [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	24,817	24,365
Current	1,061,565	1,115,378
Total loans	1,086,382	1,139,743	1,087,449
Recorded investment > 90 days and still accruing	3,610	1,230
Construction and Land Development [Member] | Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,007	19,886
Construction and Land Development [Member] | Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	126	436
Construction and Land Development [Member] | Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,684	4,043
Construction and Land Development [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,250	5,080
Total loans	2,250	5,080	14,579
Construction and Land Development [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,782	7,127
Total loans	6,782	7,127	11,482
Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	61,652	43,881
Current	7,083,754	6,951,943
Total loans	7,145,406	6,995,824	5,987,084
Recorded investment > 90 days and still accruing	2,503	3,060
Commercial Non-Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	35,443	17,406
Commercial Non-Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,843	1,468
Commercial Non-Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,366	25,007
Commercial Non-Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	61,652	43,881
Current	7,026,494	6,886,572
Total loans	7,088,146	6,930,453	5,861,887
Recorded investment > 90 days and still accruing	2,503	3,060
Commercial Non-Real Estate [Member] | Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	35,443	17,406
Commercial Non-Real Estate [Member] | Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,843	1,468
Commercial Non-Real Estate [Member] | Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,366	25,007
Commercial Non-Real Estate [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	51,949	59,843
Total loans	51,949	59,843	118,260
Commercial Non-Real Estate [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,311	5,528
Total loans	5,311	5,528	6,937
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,157	21,202
Current	3,652,935	3,391,349
Total loans	3,676,092	3,412,551	3,150,103
Recorded investment > 90 days and still accruing	1,892	1,034
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,873	6,769
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,042	1,405
Commercial Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,242	13,028
Commercial Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	22,704	20,586
Current	3,482,099	3,199,923
Total loans	3,504,803	3,220,509	2,492,351
Recorded investment > 90 days and still accruing	1,892	1,034
Commercial Real Estate [Member] | Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,873	6,754
Commercial Real Estate [Member] | Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,042	1,329
Commercial Real Estate [Member] | Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	13,789	12,503
Commercial Real Estate [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	453	616
Current	155,832	175,844
Total loans	156,285	176,460	629,975
Commercial Real Estate [Member] | Acquired Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		15
Commercial Real Estate [Member] | Acquired Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		76
Commercial Real Estate [Member] | Acquired Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	453	525
Commercial Real Estate [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,004	15,582
Total loans	15,004	15,582	27,777
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	35,634	34,857
Current	1,965,333	2,014,667
Total loans	2,000,967	2,049,524	1,913,885
Recorded investment > 90 days and still accruing	123	163
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,644	18,657
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,615	4,360
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,375	11,840
Residential Mortgages [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	35,634	34,857
Current	1,804,255	1,852,399
Total loans	1,839,889	1,887,256	1,736,033
Recorded investment > 90 days and still accruing	123	163
Residential Mortgages [Member] | Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,644	18,657
Residential Mortgages [Member] | Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,615	4,360
Residential Mortgages [Member] | Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,375	11,840
Residential Mortgages [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,116	27
Total loans	1,116	27	2,485
Residential Mortgages [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	159,962	162,241
Total loans	159,962	162,241	175,367
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,721	29,386
Current	2,036,524	2,064,079
Total loans	2,060,245	2,093,465	1,759,804
Recorded investment > 90 days and still accruing	1,098	2,166
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,050	16,309
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,500	4,432
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,171	8,645
Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,721	29,386
Current	2,024,347	2,051,240
Total loans	2,048,068	2,080,626	1,742,810
Recorded investment > 90 days and still accruing	1,098	2,166
Consumer [Member] | Originated Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14,050	16,309
Consumer [Member] | Originated Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,500	4,432
Consumer [Member] | Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,171	8,645
Consumer [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20	20
Total loans	20	20	25
Consumer [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	12,157	12,819
Total loans	$ 12,157	$ 12,819	$ 16,969