Allowance for Loan and Lease Losses (Allocation of Allowance for Loan and Lease Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	$ 1,108,379	$ 1,155,034
Allowance for loan and lease losses	223,116		$ 221,893
Loans and Leases Receivable, Net Amount	23,388,861		23,374,932
Non-PCI impaired loans less than $500,000 collectively evaluated	46,900		49,100
PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Acquired loans which have adverse change in expected cash flows	170,400		279,800
Provision for Loan, Lease, and Other Losses	2,354	(2,845)
Financing Receivable, Allowance for Credit Losses, Write-downs	84	0
Recoveries	0	0
PCI Loans | Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	310	(186)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	1,608	(1,230)
Financing Receivable, Allowance for Credit Losses, Write-downs	84	0
Recoveries	0	0
PCI Loans | Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	(46)	(158)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	13	(142)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	(50)	0
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Noncommercial | Consumer and Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	46	(34)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	264	(545)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
PCI Loans | Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan, Lease, and Other Losses	209	(550)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Recoveries	0	0
Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total impaired noncovered loans and leases	155,950		155,646
Unpaid principal balance	172,656		170,034
Impaired Financing Receivable, Related Allowance	9,866		9,728
ALLL for loans and leases individually evaluated for impairment	9,866		9,728
Impaired Financing Receivable, with Related Allowance, Recorded Investment	82,789		77,199
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	73,161		78,447
Financing Receivable, Individually Evaluated for Impairment	155,950		155,646
Average balance	155,025	136,679
Interest income recognized	1,372	1,148
Provision for Loan, Lease, and Other Losses	5,251	11,076
Financing Receivable, Allowance for Credit Losses, Write-downs	9,613	8,709
Recoveries	3,315	2,626
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	200,954		202,139
Financing Receivable, Collectively Evaluated for Impairment	22,752,190		22,678,181
Loans and Leases Receivable, Net Amount	22,908,140		22,833,827
Non-PCI Loans | Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	1,461		1,110
ALLL for loans and leases individually evaluated for impairment	171		185
Impaired Financing Receivable, with Related Allowance, Recorded Investment	740		788
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	391		0
Financing Receivable, Individually Evaluated for Impairment	1,131		788
Average balance	1,155	1,055
Interest income recognized	11	12
Provision for Loan, Lease, and Other Losses	2,225	2,536
Financing Receivable, Allowance for Credit Losses, Write-downs	0	77
Recoveries	23	55
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	26,547		24,285
Financing Receivable, Collectively Evaluated for Impairment	737,282		668,427
Loans and Leases Receivable, Net Amount	738,413		669,215
Non-PCI Loans | Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	75,584		78,936
ALLL for loans and leases individually evaluated for impairment	3,521		3,648
Impaired Financing Receivable, with Related Allowance, Recorded Investment	37,100		39,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	33,177		34,520
Financing Receivable, Individually Evaluated for Impairment	70,277		73,655
Average balance	72,267	75,310
Interest income recognized	711	642
Provision for Loan, Lease, and Other Losses	(1,365)	6
Financing Receivable, Allowance for Credit Losses, Write-downs	46	37
Recoveries	239	364
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	40,312		41,357
Financing Receivable, Collectively Evaluated for Impairment	9,788,859		9,655,367
Loans and Leases Receivable, Net Amount	9,859,136		9,729,022
Non-PCI Loans | Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	1,614		2,267
ALLL for loans and leases individually evaluated for impairment	306		209
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,086		1,351
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	413		506
Financing Receivable, Individually Evaluated for Impairment	1,499		1,857
Average balance	1,713	1,584
Interest income recognized	11	8
Provision for Loan, Lease, and Other Losses	(1,293)	304
Financing Receivable, Allowance for Credit Losses, Write-downs	0	5
Recoveries	145	4
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,117		4,362
Financing Receivable, Collectively Evaluated for Impairment	385,235		471,576
Loans and Leases Receivable, Net Amount	386,734		473,433
Non-PCI Loans | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	10,882		10,475
ALLL for loans and leases individually evaluated for impairment	621		665
Impaired Financing Receivable, with Related Allowance, Recorded Investment	5,514		6,326
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,097		1,648
Financing Receivable, Individually Evaluated for Impairment	7,611		7,974
Average balance	7,524	11,529
Interest income recognized	76	104
Provision for Loan, Lease, and Other Losses	(425)	3,592
Financing Receivable, Allowance for Credit Losses, Write-downs	1,475	3,253
Recoveries	1,219	265
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	52,395		53,032
Financing Receivable, Collectively Evaluated for Impairment	2,687,594		2,722,433
Loans and Leases Receivable, Net Amount	2,695,205		2,730,407
Non-PCI Loans | Commercial | Lease financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,610		2,571
ALLL for loans and leases individually evaluated for impairment	494		397
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,896		1,890
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	270		24
Financing Receivable, Individually Evaluated for Impairment	2,166		1,914
Average balance	2,238	1,568
Interest income recognized	11	14
Provision for Loan, Lease, and Other Losses	987	575
Financing Receivable, Allowance for Credit Losses, Write-downs	854	173
Recoveries	41	6
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5,807		5,730
Financing Receivable, Collectively Evaluated for Impairment	908,423		892,887
Loans and Leases Receivable, Net Amount	910,589		894,801
Non-PCI Loans | Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance			521
ALLL for loans and leases individually evaluated for impairment	0		0
Impaired Financing Receivable, with Related Allowance, Recorded Investment			0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			521
Financing Receivable, Individually Evaluated for Impairment	0		521
Average balance	0	196
Interest income recognized	0	2
Provision for Loan, Lease, and Other Losses	114	517
Financing Receivable, Allowance for Credit Losses, Write-downs	3	123
Recoveries	42	13
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,842		4,689
Financing Receivable, Collectively Evaluated for Impairment	281,485		301,655
Loans and Leases Receivable, Net Amount	281,485		302,176
Non-PCI Loans | Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	4,620		5,224
ALLL for loans and leases individually evaluated for impairment	82		68
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,294		592
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,509		3,959
Financing Receivable, Individually Evaluated for Impairment	3,803		4,551
Average balance	4,104	2,605
Interest income recognized	48	33
Provision for Loan, Lease, and Other Losses	107	(83)
Financing Receivable, Allowance for Credit Losses, Write-downs	182	0
Recoveries	26	0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,831		3,894
Financing Receivable, Collectively Evaluated for Impairment	239,311		243,738
Loans and Leases Receivable, Net Amount	243,114		248,289
Non-PCI Loans | Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	44,065		39,946
ALLL for loans and leases individually evaluated for impairment	2,905		2,733
Impaired Financing Receivable, with Related Allowance, Recorded Investment	23,417		19,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	17,930		18,707
Financing Receivable, Individually Evaluated for Impairment	41,347		37,842
Average balance	38,724	32,963
Interest income recognized	275	253
Provision for Loan, Lease, and Other Losses	1,512	1,351
Financing Receivable, Allowance for Credit Losses, Write-downs	806	250
Recoveries	77	287
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	13,584		12,973
Financing Receivable, Collectively Evaluated for Impairment	3,546,444		3,485,944
Loans and Leases Receivable, Net Amount	3,587,791		3,523,786
Non-PCI Loans | Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	27,948		25,941
ALLL for loans and leases individually evaluated for impairment	1,053		1,085
Impaired Financing Receivable, with Related Allowance, Recorded Investment	9,998		5,875
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15,527		17,895
Financing Receivable, Individually Evaluated for Impairment	25,525		23,770
Average balance	24,792	7,969
Interest income recognized	201	57
Provision for Loan, Lease, and Other Losses	466	550
Financing Receivable, Allowance for Credit Losses, Write-downs	992	825
Recoveries	194	552
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	21,051		21,351
Financing Receivable, Collectively Evaluated for Impairment	2,626,123		2,677,755
Loans and Leases Receivable, Net Amount	2,651,648		2,701,525
Non-PCI Loans | Noncommercial | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	2,872		3,043
ALLL for loans and leases individually evaluated for impairment	713		738
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,744		2,107
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	847		667
Financing Receivable, Individually Evaluated for Impairment	2,591		2,774
Average balance	2,508	1,900
Interest income recognized	28	23
Provision for Loan, Lease, and Other Losses	2,923	1,728
Financing Receivable, Allowance for Credit Losses, Write-downs	5,255	3,966
Recoveries	1,309	$ 1,080
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	29,468		30,466
Financing Receivable, Collectively Evaluated for Impairment	1,551,434		1,558,399
Loans and Leases Receivable, Net Amount	$ 1,554,025		$ 1,561,173