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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 164,857		$ 164,857		$ 156,130
Unpaid principal balance	805,754	$ 1,044,148	805,754	$ 1,044,148
Loans and Leases Receivable, Net Amount	26,501,654		26,501,654		25,299,564
Non-PCI impaired loans less than $500,000 collectively evaluated	39,900		39,900		47,100
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	74,470		74,470		74,560
Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	2,193		2,193		2,298
Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	59,260		59,260		61,065
Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	506		506		860
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	12,196		12,196		10,046
Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	315		315		291
Noncommercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	90,387		90,387		81,570
Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	3,060		3,060		2,337
Noncommercial | Consumer and Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	3,106		3,106		3,021
Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	54,099		54,099		47,524
Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	30,122		30,122		28,688
PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Recorded Investment	18,000		18,000		18,200
Acquired loans which have adverse change in expected cash flows	163,900		163,900		186,600
Provision for Loan, Lease, and Other Losses	(637)	161	(801)	2,515
Financing Receivable, Allowance for Credit Losses, Write-downs	0	34	0	118
Recoveries	0	0	0	0
Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	186,055		186,055		163,902
ALLL for loans and leases individually evaluated for impairment	11,098		11,098		9,827
Impaired Financing Receivable, with Related Allowance, Recorded Investment	121,996		121,996		115,073
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	44,677		44,677		31,357
Financing Receivable, Individually Evaluated for Impairment	166,673		166,673		146,430
Average balance	157,877	155,051	152,886	155,038
Interest income recognized	1,301	1,370	2,640	2,742
Provision for Loan, Lease, and Other Losses	5,835	8,277	17,749	13,528
Financing Receivable, Allowance for Credit Losses, Write-downs	(10,602)	(9,678)	(20,756)	(19,291)
Recoveries	3,212	3,023	6,679	6,338
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	207,142		207,142		204,741
Financing Receivable, Collectively Evaluated for Impairment	26,010,117		26,010,117		24,770,270
Loans and Leases Receivable, Net Amount	26,176,790		26,176,790		24,916,700
Non-PCI Loans | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	89,231		89,231
ALLL for loans and leases individually evaluated for impairment	4,775		4,775
Impaired Financing Receivable, with Related Allowance, Recorded Investment	47,857		47,857
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	29,473		29,473
Financing Receivable, Individually Evaluated for Impairment	77,330		77,330
Average balance	73,203	80,437	71,491	82,667
Interest income recognized	665	778	1,367	1,598
Non-PCI Loans | Commercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	2,490		2,490		2,606
ALLL for loans and leases individually evaluated for impairment	196		196		490
Impaired Financing Receivable, with Related Allowance, Recorded Investment	463		463		1,897
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,615		1,615		278
Financing Receivable, Individually Evaluated for Impairment	2,078		2,078		2,175
Average balance	2,102	1,485	2,125	1,320
Interest income recognized	6	17	34	28
Provision for Loan, Lease, and Other Losses	(5,544)	(3,139)	(3,425)	(914)
Financing Receivable, Allowance for Credit Losses, Write-downs	(28)	(8)	(72)	(8)
Recoveries	40	93	171	116
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	31,748		31,748		34,780
Financing Receivable, Collectively Evaluated for Impairment	717,456		717,456		755,679
Loans and Leases Receivable, Net Amount	719,534		719,534		757,854
Non-PCI Loans | Commercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	68,477		68,477		61,317
ALLL for loans and leases individually evaluated for impairment	3,042		3,042		2,671
Impaired Financing Receivable, with Related Allowance, Recorded Investment	38,793		38,793		34,177
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	23,477		23,477		21,270
Financing Receivable, Individually Evaluated for Impairment	62,270		62,270		55,447
Average balance	58,906	68,113	57,768	70,190
Interest income recognized	538	659	1,102	1,370
Provision for Loan, Lease, and Other Losses	3,714	866	6,085	(499)
Financing Receivable, Allowance for Credit Losses, Write-downs	(89)	(459)	(850)	(505)
Recoveries	56	225	276	464
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	45,920		45,920		40,780
Financing Receivable, Collectively Evaluated for Impairment	11,274,414		11,274,414		10,661,787
Loans and Leases Receivable, Net Amount	11,336,684		11,336,684		10,717,234
Non-PCI Loans | Commercial | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	595		595		946
ALLL for loans and leases individually evaluated for impairment	11		11		42
Impaired Financing Receivable, with Related Allowance, Recorded Investment	197		197		243
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	309		309		617
Financing Receivable, Individually Evaluated for Impairment	506		506		860
Average balance	519	1,345	602	1,529
Interest income recognized	6	12	14	23
Provision for Loan, Lease, and Other Losses	(57)	468	(140)	(825)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(69)	0	(69)
Recoveries	0	1	1	146
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,331		2,331		2,439
Financing Receivable, Collectively Evaluated for Impairment	506,254		506,254		426,125
Loans and Leases Receivable, Net Amount	506,760		506,760		426,985
Non-PCI Loans | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	17,333		17,333		14,695
ALLL for loans and leases individually evaluated for impairment	1,422		1,422		1,137
Impaired Financing Receivable, with Related Allowance, Recorded Investment	8,155		8,155		7,153
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,006		4,006		2,715
Financing Receivable, Individually Evaluated for Impairment	12,161		12,161		9,868
Average balance	11,348	9,427	10,674	9,594
Interest income recognized	113	90	213	177
Provision for Loan, Lease, and Other Losses	2,699	3,791	5,424	4,353
Financing Receivable, Allowance for Credit Losses, Write-downs	(3,422)	(2,439)	(5,280)	(4,768)
Recoveries	599	642	1,137	1,902
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	55,479		55,479		54,483
Financing Receivable, Collectively Evaluated for Impairment	3,968,343		3,968,343		3,928,862
Loans and Leases Receivable, Net Amount	3,980,504		3,980,504		3,938,730
Non-PCI Loans | Commercial | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	336		336		301
ALLL for loans and leases individually evaluated for impairment	104		104		105
Impaired Financing Receivable, with Related Allowance, Recorded Investment	249		249		216
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	66		66		75
Financing Receivable, Individually Evaluated for Impairment	315		315		291
Average balance	328	67	322	34
Interest income recognized	2	0	4	0
Provision for Loan, Lease, and Other Losses	(174)	(114)	(672)	0
Financing Receivable, Allowance for Credit Losses, Write-downs	(31)	(38)	(31)	(41)
Recoveries	221	1	665	43
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,079		2,079		2,116
Financing Receivable, Collectively Evaluated for Impairment	301,031		301,031		296,133
Loans and Leases Receivable, Net Amount	301,346		301,346		296,424
Non-PCI Loans | Noncommercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	96,824		96,824
ALLL for loans and leases individually evaluated for impairment	6,323		6,323
Impaired Financing Receivable, with Related Allowance, Recorded Investment	74,139		74,139
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15,204		15,204
Financing Receivable, Individually Evaluated for Impairment	89,343		89,343
Average balance	84,674	74,614	81,395	72,371
Interest income recognized	636	592	1,273	1,144
Non-PCI Loans | Noncommercial | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,353		3,353		4,035
ALLL for loans and leases individually evaluated for impairment	82		82		81
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,647		1,647		2,337
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,412		1,412		1,412
Financing Receivable, Individually Evaluated for Impairment	3,059		3,059		3,749
Average balance	3,547	3,526	3,647	3,815
Interest income recognized	32	44	68	92
Provision for Loan, Lease, and Other Losses	277	50	400	157
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(37)	0	(219)
Recoveries	0	101	0	127
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,668		2,668		2,269
Financing Receivable, Collectively Evaluated for Impairment	312,012		312,012		253,281
Loans and Leases Receivable, Net Amount	315,071		315,071		257,030
Non-PCI Loans | Noncommercial | Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	56,860		56,860		45,226
ALLL for loans and leases individually evaluated for impairment	2,566		2,566		1,901
Impaired Financing Receivable, with Related Allowance, Recorded Investment	43,349		43,349		40,359
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	9,788		9,788		1,809
Financing Receivable, Individually Evaluated for Impairment	53,137		53,137		42,168
Average balance	48,490	42,046	45,558	40,385
Interest income recognized	317	298	642	573
Provision for Loan, Lease, and Other Losses	371	1,492	1,879	3,004
Financing Receivable, Allowance for Credit Losses, Write-downs	(478)	(289)	(644)	(1,095)
Recoveries	52	110	225	187
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	14,366		14,366		13,571
Financing Receivable, Collectively Evaluated for Impairment	4,737,499		4,737,499		4,223,519
Loans and Leases Receivable, Net Amount	4,790,636		4,790,636		4,265,687
Non-PCI Loans | Noncommercial | Revolving mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	33,135		33,135		31,371
ALLL for loans and leases individually evaluated for impairment	2,704		2,704		2,515
Impaired Financing Receivable, with Related Allowance, Recorded Investment	26,104		26,104		25,751
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,936		3,936		3,101
Financing Receivable, Individually Evaluated for Impairment	30,040		30,040		28,852
Average balance	29,623	26,388	29,183	25,590
Interest income recognized	256	222	503	423
Provision for Loan, Lease, and Other Losses	(328)	289	(119)	755
Financing Receivable, Allowance for Credit Losses, Write-downs	(493)	(1,027)	(1,456)	(2,019)
Recoveries	447	520	834	714
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	18,417		18,417		19,347
Financing Receivable, Collectively Evaluated for Impairment	2,440,613		2,440,613		2,514,123
Loans and Leases Receivable, Net Amount	2,470,653		2,470,653		2,542,975
Non-PCI Loans | Noncommercial | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Unpaid principal balance	3,476		3,476		3,405
ALLL for loans and leases individually evaluated for impairment	971		971		885
Impaired Financing Receivable, with Related Allowance, Recorded Investment	3,039		3,039		2,940
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	68		68		80
Financing Receivable, Individually Evaluated for Impairment	3,107		3,107		3,020
Average balance	3,014	2,654	3,007	2,581
Interest income recognized	31	28	60	56
Provision for Loan, Lease, and Other Losses	4,877	4,574	8,317	7,497
Financing Receivable, Allowance for Credit Losses, Write-downs	(6,061)	(5,312)	(12,423)	(10,567)
Recoveries	1,797	$ 1,330	3,370	$ 2,639
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	34,134		34,134		34,956
Financing Receivable, Collectively Evaluated for Impairment	1,752,495		1,752,495		1,710,761
Loans and Leases Receivable, Net Amount	$ 1,755,602		$ 1,755,602		$ 1,713,781