Allowance for Loan and Lease Losses (Allocation of Allowance for Loan and Lease Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	$ 1,044,148	$ 1,199,358	$ 1,044,148	$ 1,199,358
Allowance for loan and lease losses	224,865		224,865		$ 221,893
Loans and Leases Receivable, Net Amount	24,313,572		24,313,572		23,374,932
Non-PCI impaired loans less than $500,000 collectively evaluated	44,100		44,100		49,100
PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Acquired loans which have adverse change in expected cash flows	160,800		160,800		279,800
Provision for Loan, Lease, and Other Losses	161	2,572	2,515	(273)
Financing Receivable, Allowance for Credit Losses, Write-downs	34	0	118	0
Recoveries	0	0	0	0
Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total impaired noncovered loans and leases	155,228		155,228		155,646
Unpaid principal balance	174,460		174,460		170,034
Impaired Financing Receivable, Related Allowance	10,001		10,001		9,728
ALLL for loans and leases individually evaluated for impairment	10,001		10,001		9,728
Impaired Financing Receivable, with Related Allowance, Recorded Investment	83,622		83,622		77,199
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	71,606		71,606		78,447
Financing Receivable, Individually Evaluated for Impairment	155,228		155,228		155,646
Average balance	155,051	139,608	155,038	138,144
Interest income recognized	1,370	1,179	2,742	2,327
Provision for Loan, Lease, and Other Losses	8,277	9,752	13,528	20,828
Financing Receivable, Allowance for Credit Losses, Write-downs	9,678	9,423	19,291	18,194
Recoveries	3,023	4,954	6,338	7,642
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	202,441		202,441		202,139
Financing Receivable, Collectively Evaluated for Impairment	23,708,940		23,708,940		22,678,181
Loans and Leases Receivable, Net Amount	23,864,168		23,864,168		22,833,827
Non-PCI Loans | Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	2,431		2,431		1,110
ALLL for loans and leases individually evaluated for impairment	274		274		185
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,098		2,098		788
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0		0		0
Financing Receivable, Individually Evaluated for Impairment	2,098		2,098		788
Average balance	1,485	970	1,320	1,013
Interest income recognized	17	11	28	23
Provision for Loan, Lease, and Other Losses	(3,139)	2,372	(914)	4,908
Financing Receivable, Allowance for Credit Losses, Write-downs	8	413	8	490
Recoveries	93	209	116	264
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	23,390		23,390		24,285
Financing Receivable, Collectively Evaluated for Impairment	712,913		712,913		668,427
Loans and Leases Receivable, Net Amount	715,011		715,011		669,215
Non-PCI Loans | Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	72,467		72,467		78,936
ALLL for loans and leases individually evaluated for impairment	3,325		3,325		3,648
Impaired Financing Receivable, with Related Allowance, Recorded Investment	35,934		35,934		39,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	30,238		30,238		34,520
Financing Receivable, Individually Evaluated for Impairment	66,172		66,172		73,655
Average balance	68,113	74,121	70,190	74,715
Interest income recognized	659	651	1,370	1,293
Provision for Loan, Lease, and Other Losses	866	639	(499)	645
Financing Receivable, Allowance for Credit Losses, Write-downs	459	235	505	272
Recoveries	225	731	464	1,095
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	41,140		41,140		41,357
Financing Receivable, Collectively Evaluated for Impairment	10,212,569		10,212,569		9,655,367
Loans and Leases Receivable, Net Amount	10,278,741		10,278,741		9,729,022
Non-PCI Loans | Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	1,264		1,264		2,267
ALLL for loans and leases individually evaluated for impairment	65		65		209
Impaired Financing Receivable, with Related Allowance, Recorded Investment	375		375		1,351
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	702		702		506
Financing Receivable, Individually Evaluated for Impairment	1,077		1,077		1,857
Average balance	1,345	1,525	1,529	1,555
Interest income recognized	12	9	23	17
Provision for Loan, Lease, and Other Losses	468	33	(825)	337
Financing Receivable, Allowance for Credit Losses, Write-downs	69	0	69	5
Recoveries	1	7	146	11
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,758		3,758		4,362
Financing Receivable, Collectively Evaluated for Impairment	472,375		472,375		471,576
Loans and Leases Receivable, Net Amount	473,452		473,452		473,433
Non-PCI Loans | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	11,684		11,684		10,475
ALLL for loans and leases individually evaluated for impairment	985		985		665
Impaired Financing Receivable, with Related Allowance, Recorded Investment	6,262		6,262		6,326
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,390		1,390		1,648
Financing Receivable, Individually Evaluated for Impairment	7,652		7,652		7,974
Average balance	7,585	10,159	7,554	10,844
Interest income recognized	76	98	152	202
Provision for Loan, Lease, and Other Losses	5,670	968	5,245	4,560
Financing Receivable, Allowance for Credit Losses, Write-downs	1,994	3,121	3,469	6,374
Recoveries	638	2,392	1,857	2,657
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	56,345		56,345		53,032
Financing Receivable, Collectively Evaluated for Impairment	3,089,889		3,089,889		2,722,433
Loans and Leases Receivable, Net Amount	3,097,541		3,097,541		2,730,407
Non-PCI Loans | Commercial | Lease financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	2,808		2,808		2,571
ALLL for loans and leases individually evaluated for impairment	107		107		397
Impaired Financing Receivable, with Related Allowance, Recorded Investment	789		789		1,890
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	387		387		24
Financing Receivable, Individually Evaluated for Impairment	1,176		1,176		1,914
Average balance	1,842	1,911	2,040	1,740
Interest income recognized	14	14	25	28
Provision for Loan, Lease, and Other Losses	(1,879)	186	(892)	761
Financing Receivable, Allowance for Credit Losses, Write-downs	445	97	1,299	270
Recoveries	4	0	45	6
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,874		3,874		5,730
Financing Receivable, Collectively Evaluated for Impairment	612,201		612,201		892,887
Loans and Leases Receivable, Net Amount	613,377		613,377		894,801
Non-PCI Loans | Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	315		315		521
ALLL for loans and leases individually evaluated for impairment	20		20		0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	97		97		0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0		0		521
Financing Receivable, Individually Evaluated for Impairment	97		97		521
Average balance	67	434	34	315
Interest income recognized	0	5	0	7
Provision for Loan, Lease, and Other Losses	(114)	(214)	0	241
Financing Receivable, Allowance for Credit Losses, Write-downs	38	64	41	187
Recoveries	1	46	43	121
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,671		4,671		4,689
Financing Receivable, Collectively Evaluated for Impairment	296,517		296,517		301,655
Loans and Leases Receivable, Net Amount	296,614		296,614		302,176
Non-PCI Loans | Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,633		3,633		5,224
ALLL for loans and leases individually evaluated for impairment	66		66		68
Impaired Financing Receivable, with Related Allowance, Recorded Investment	544		544		592
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,367		2,367		3,959
Financing Receivable, Individually Evaluated for Impairment	2,911		2,911		4,551
Average balance	3,526	3,185	3,815	2,895
Interest income recognized	44	33	92	66
Provision for Loan, Lease, and Other Losses	50	(10)	157	(93)
Financing Receivable, Allowance for Credit Losses, Write-downs	37	0	219	0
Recoveries	101	0	127	0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,961		3,961		3,894
Financing Receivable, Collectively Evaluated for Impairment	247,793		247,793		243,738
Loans and Leases Receivable, Net Amount	250,704		250,704		248,289
Non-PCI Loans | Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	46,684		46,684		39,946
ALLL for loans and leases individually evaluated for impairment	3,343		3,343		2,733
Impaired Financing Receivable, with Related Allowance, Recorded Investment	25,529		25,529		19,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	18,424		18,424		18,707
Financing Receivable, Individually Evaluated for Impairment	43,953		43,953		37,842
Average balance	42,046	36,767	40,385	34,864
Interest income recognized	298	272	573	525
Provision for Loan, Lease, and Other Losses	1,492	155	3,004	1,506
Financing Receivable, Allowance for Credit Losses, Write-downs	289	222	1,095	472
Recoveries	110	75	187	362
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	14,459		14,459		12,973
Financing Receivable, Collectively Evaluated for Impairment	3,936,892		3,936,892		3,485,944
Loans and Leases Receivable, Net Amount	3,980,845		3,980,845		3,523,786
Non-PCI Loans | Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	30,170		30,170		25,941
ALLL for loans and leases individually evaluated for impairment	1,112		1,112		1,085
Impaired Financing Receivable, with Related Allowance, Recorded Investment	10,217		10,217		5,875
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	17,190		17,190		17,895
Financing Receivable, Individually Evaluated for Impairment	27,407		27,407		23,770
Average balance	26,388	8,484	25,590	8,227
Interest income recognized	222	62	423	119
Provision for Loan, Lease, and Other Losses	289	1,054	755	1,604
Financing Receivable, Allowance for Credit Losses, Write-downs	1,027	280	2,019	1,105
Recoveries	520	401	714	953
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	20,774		20,774		21,351
Financing Receivable, Collectively Evaluated for Impairment	2,577,548		2,577,548		2,677,755
Loans and Leases Receivable, Net Amount	2,604,955		2,604,955		2,701,525
Non-PCI Loans | Noncommercial | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,004		3,004		3,043
ALLL for loans and leases individually evaluated for impairment	704		704		738
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,777		1,777		2,107
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	908		908		667
Financing Receivable, Individually Evaluated for Impairment	2,685		2,685		2,774
Average balance	2,654	2,052	2,581	1,976
Interest income recognized	28	24	56	47
Provision for Loan, Lease, and Other Losses	4,574	4,569	7,497	6,359
Financing Receivable, Allowance for Credit Losses, Write-downs	5,312	4,991	10,567	9,019
Recoveries	1,330	$ 1,093	2,639	$ 2,173
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	30,069		30,069		30,466
Financing Receivable, Collectively Evaluated for Impairment	1,550,243		1,550,243		1,558,399
Loans and Leases Receivable, Net Amount	$ 1,552,928		$ 1,552,928		$ 1,561,173