Allowance for Loan and Lease Losses (Allocation of Allowance for Loan and Lease Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 161,971		$ 161,971		$ 164,561
Unpaid principal balance	999,926	$ 1,293,760	999,926	$ 1,293,760
Loans and Leases Receivable, Net Amount	24,667,150		24,667,150		23,374,932
Non-PCI impaired loans less than $500,000 collectively evaluated	43,800		43,800		49,100
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	81,451		81,451		95,392
Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	2,350		2,350		4,572
Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	67,664		67,664		78,221
Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	929		929		1,800
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	9,319		9,319		8,508
Commercial | Lease financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	947		947		1,770
Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	242		242		521
Noncommercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	80,520		80,520		69,169
Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	2,824		2,824		0
Noncommercial | Consumer and Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	2,887		2,887		2,774
Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	46,892		46,892		43,542
Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	27,917		27,917		22,853
PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	18,369		18,369		18,400
Acquired loans which have adverse change in expected cash flows	190,800		190,800		279,800
Provision for Loan, Lease, and Other Losses	(1,514)	(537)	1,000	(810)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	117	0
Recoveries	0	0	0	0
Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total impaired noncovered loans and leases	154,676		154,676		155,646
Unpaid principal balance	174,111		174,111		170,034
Impaired Financing Receivable, Related Allowance	11,425		11,425		9,728
ALLL for loans and leases individually evaluated for impairment	11,425		11,425		9,728
Impaired Financing Receivable, with Related Allowance, Recorded Investment	116,919		116,919		77,199
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	37,757		37,757		78,447
Financing Receivable, Individually Evaluated for Impairment	154,676		154,676		155,646
Average balance	152,381	142,648	154,152	139,645
Interest income recognized	1,350	1,225	4,092	3,552
Provision for Loan, Lease, and Other Losses	2,354	8,483	15,883	29,311
Financing Receivable, Allowance for Credit Losses, Write-downs	9,447	8,494	28,739	26,688
Recoveries	2,939	3,592	9,277	11,234
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	196,863		196,863		202,139
Financing Receivable, Collectively Evaluated for Impairment	24,093,653		24,093,653		22,678,181
Loans and Leases Receivable, Net Amount	24,248,329		24,248,329		22,833,827
Non-PCI Loans | Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	2,600		2,600		1,110
ALLL for loans and leases individually evaluated for impairment	296		296		185
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,175		2,175		788
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0		0		0
Financing Receivable, Individually Evaluated for Impairment	2,175		2,175		788
Average balance	2,101	754	1,580	926
Interest income recognized	27	8	55	31
Provision for Loan, Lease, and Other Losses	8,702	(5,150)	7,788	(242)
Financing Receivable, Allowance for Credit Losses, Write-downs	35	9	43	499
Recoveries	136	56	252	320
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	32,171		32,171		24,285
Financing Receivable, Collectively Evaluated for Impairment	677,028		677,028		668,427
Loans and Leases Receivable, Net Amount	679,203		679,203		669,215
Non-PCI Loans | Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	70,501		70,501		78,936
ALLL for loans and leases individually evaluated for impairment	2,983		2,983		3,648
Impaired Financing Receivable, with Related Allowance, Recorded Investment	34,860		34,860		39,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	28,552		28,552		34,520
Financing Receivable, Individually Evaluated for Impairment	63,412		63,412		73,655
Average balance	63,752	73,099	68,043	74,177
Interest income recognized	583	653	1,953	1,946
Provision for Loan, Lease, and Other Losses	(2,870)	(71)	(3,369)	574
Financing Receivable, Allowance for Credit Losses, Write-downs	606	39	1,111	311
Recoveries	99	1,446	563	2,541
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	38,105		38,105		41,357
Financing Receivable, Collectively Evaluated for Impairment	10,422,960		10,422,960		9,655,367
Loans and Leases Receivable, Net Amount	10,486,372		10,486,372		9,729,022
Non-PCI Loans | Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	1,104		1,104		2,267
ALLL for loans and leases individually evaluated for impairment	46		46		209
Impaired Financing Receivable, with Related Allowance, Recorded Investment	199		199		1,351
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	730		730		506
Financing Receivable, Individually Evaluated for Impairment	929		929		1,857
Average balance	950	1,720	1,336	1,610
Interest income recognized	10	8	33	25
Provision for Loan, Lease, and Other Losses	(1,219)	891	(2,044)	1,228
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	69	5
Recoveries	1	8	147	19
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,559		2,559		4,362
Financing Receivable, Collectively Evaluated for Impairment	470,603		470,603		471,576
Loans and Leases Receivable, Net Amount	471,532		471,532		473,433
Non-PCI Loans | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	14,050		14,050		10,475
ALLL for loans and leases individually evaluated for impairment	1,133		1,133		665
Impaired Financing Receivable, with Related Allowance, Recorded Investment	6,573		6,573		6,326
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,475		2,475		1,648
Financing Receivable, Individually Evaluated for Impairment	9,048		9,048		7,974
Average balance	8,278	9,501	7,796	10,396
Interest income recognized	83	96	235	298
Provision for Loan, Lease, and Other Losses	(9,271)	5,621	(4,026)	10,181
Financing Receivable, Allowance for Credit Losses, Write-downs	1,256	1,275	4,725	7,649
Recoveries	494	433	2,351	3,090
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	46,164		46,164		53,032
Financing Receivable, Collectively Evaluated for Impairment	3,180,289		3,180,289		2,722,433
Loans and Leases Receivable, Net Amount	3,189,337		3,189,337		2,730,407
Non-PCI Loans | Commercial | Lease financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	1,894		1,894		2,571
ALLL for loans and leases individually evaluated for impairment	135		135		397
Impaired Financing Receivable, with Related Allowance, Recorded Investment	755		755		1,890
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	287		287		24
Financing Receivable, Individually Evaluated for Impairment	1,042		1,042		1,914
Average balance	1,032	1,752	1,704	1,744
Interest income recognized	9	12	34	40
Provision for Loan, Lease, and Other Losses	4,011	884	3,119	1,645
Financing Receivable, Allowance for Credit Losses, Write-downs	850	687	2,149	957
Recoveries	3	3	48	9
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7,010		7,010		5,730
Financing Receivable, Collectively Evaluated for Impairment	615,909		615,909		892,887
Loans and Leases Receivable, Net Amount	616,951		616,951		894,801
Non-PCI Loans | Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	246		246		521
ALLL for loans and leases individually evaluated for impairment	18		18		0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	241		241		0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0		0		521
Financing Receivable, Individually Evaluated for Impairment	241		241		521
Average balance	205	557	90	396
Interest income recognized	1	8	1	15
Provision for Loan, Lease, and Other Losses	(2,404)	58	(2,403)	299
Financing Receivable, Allowance for Credit Losses, Write-downs	56	666	98	853
Recoveries	117	123	160	244
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,330		2,330		4,689
Financing Receivable, Collectively Evaluated for Impairment	296,747		296,747		301,655
Loans and Leases Receivable, Net Amount	296,988		296,988		302,176
Non-PCI Loans | Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	4,527		4,527		5,224
ALLL for loans and leases individually evaluated for impairment	501		501		68
Impaired Financing Receivable, with Related Allowance, Recorded Investment	4,236		4,236		592
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0		0		3,959
Financing Receivable, Individually Evaluated for Impairment	4,236		4,236		4,551
Average balance	3,190	3,676	3,607	3,155
Interest income recognized	42	35	134	101
Provision for Loan, Lease, and Other Losses	(1,203)	92	(1,046)	(1)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	219	0
Recoveries	0	0	127	0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,323		2,323		3,894
Financing Receivable, Collectively Evaluated for Impairment	237,200		237,200		243,738
Loans and Leases Receivable, Net Amount	241,436		241,436		248,289
Non-PCI Loans | Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	45,528		45,528		39,946
ALLL for loans and leases individually evaluated for impairment	2,791		2,791		2,733
Impaired Financing Receivable, with Related Allowance, Recorded Investment	40,128		40,128		19,135
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,489		2,489		18,707
Financing Receivable, Individually Evaluated for Impairment	42,617		42,617		37,842
Average balance	42,601	31,290	41,124	33,673
Interest income recognized	330	228	903	753
Provision for Loan, Lease, and Other Losses	(1,828)	531	1,176	2,037
Financing Receivable, Allowance for Credit Losses, Write-downs	360	604	1,455	1,076
Recoveries	128	92	315	454
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	12,951		12,951		12,973
Financing Receivable, Collectively Evaluated for Impairment	4,030,618		4,030,618		3,485,944
Loans and Leases Receivable, Net Amount	4,073,235		4,073,235		3,523,786
Non-PCI Loans | Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	30,463		30,463		25,941
ALLL for loans and leases individually evaluated for impairment	2,759		2,759		1,085
Impaired Financing Receivable, with Related Allowance, Recorded Investment	24,953		24,953		5,875
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,136		3,136		17,895
Financing Receivable, Individually Evaluated for Impairment	28,089		28,089		23,770
Average balance	27,503	18,066	26,228	11,506
Interest income recognized	234	150	657	269
Provision for Loan, Lease, and Other Losses	465	842	1,220	2,446
Financing Receivable, Allowance for Credit Losses, Write-downs	759	218	2,778	1,323
Recoveries	712	228	1,426	1,181
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	19,545		19,545		21,351
Financing Receivable, Collectively Evaluated for Impairment	2,542,007		2,542,007		2,677,755
Loans and Leases Receivable, Net Amount	2,570,096		2,570,096		2,701,525
Non-PCI Loans | Noncommercial | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,198		3,198		3,043
ALLL for loans and leases individually evaluated for impairment	763		763		738
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,799		2,799		2,107
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	88		88		667
Financing Receivable, Individually Evaluated for Impairment	2,887		2,887		2,774
Average balance	2,769	2,233	2,644	2,062
Interest income recognized	31	27	87	74
Provision for Loan, Lease, and Other Losses	7,971	4,785	15,468	11,144
Financing Receivable, Allowance for Credit Losses, Write-downs	5,525	4,996	16,092	14,015
Recoveries	1,249	$ 1,203	3,888	$ 3,376
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	33,705		33,705		30,466
Financing Receivable, Collectively Evaluated for Impairment	1,620,292		1,620,292		1,558,399
Loans and Leases Receivable, Net Amount	$ 1,623,179		$ 1,623,179		$ 1,561,173