Loans and Allowance for Credit Losses (Allowance for Credit Losses by Portfolio Class) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			$ 450,177	$ 191,251
Allowance for loan losses: Cumulative effect of change in accounting principle				27,330
Allowance for loan losses: Net provision for loan losses	$ (17,229)	$ 306,898	(22,140)	553,691
Allowance for loan losses: Ending balance	399,668	442,638	399,668	442,638
Reserve for unfunded lending commitments: Beginning balance			29,907	3,974
Reserve for unfunded lending commitments: Provision for losses			(383)	5,267
Reserve for unfunded lending commitments: Ending balance	29,524	36,571	29,524	36,571
Total allowance for credit losses	429,192	479,209	429,192	479,209
Allowance for loan losses: Individually evaluated	4,027	15,222	4,027	15,222
Allowance for loan losses: Collectively evaluated	395,641	427,416	395,641	427,416
Reserve for unfunded lending commitments: Individually evaluated	241	751	241	751
Reserve for unfunded lending commitments: Collectively evaluated	29,283	35,820	29,283	35,820
Loans: Individually evaluated for impairment	33,878	116,205	33,878	116,205
Loans: Collectively evaluated for impairment	21,114,652	22,512,172	21,114,652	22,512,172
Loans receivable	21,148,530	22,628,377	21,148,530	22,628,377	$ 21,789,931
Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				49,411
Allowance for loan losses: Charge-offs			(37,926)	(353,655)
Allowance for loan losses: Recoveries			9,174	7,207
Allowance for loan losses: Net provision for loan losses			(21,757)	548,424
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			109,474	20,869
Allowance for loan losses: Cumulative effect of change in accounting principle				449
Allowance for loan losses: Ending balance	123,780	97,911	123,780	97,911
Reserve for unfunded lending commitments: Beginning balance			1,099
Reserve for unfunded lending commitments: Provision for losses			244	649
Reserve for unfunded lending commitments: Ending balance	1,343	1,098	1,343	1,098
Total allowance for credit losses	125,123	99,009	125,123	99,009
Allowance for loan losses: Individually evaluated	21	457	21	457
Allowance for loan losses: Collectively evaluated	123,759	97,454	123,759	97,454
Reserve for unfunded lending commitments: Collectively evaluated	1,343	1,098	1,343	1,098
Loans: Individually evaluated for impairment	4,018	6,222	4,018	6,222
Loans: Collectively evaluated for impairment	3,415,010	3,344,077	3,415,010	3,344,077
Loans receivable	3,419,028	3,350,299	3,419,028	3,350,299	3,357,939
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			26,462	9,350
Allowance for loan losses: Cumulative effect of change in accounting principle				15,658
Allowance for loan losses: Ending balance	26,728	31,239	26,728	31,239
Reserve for unfunded lending commitments: Beginning balance			22,694
Reserve for unfunded lending commitments: Provision for losses			(1,470)	10,455
Reserve for unfunded lending commitments: Ending balance	21,224	26,113	21,224	26,113
Total allowance for credit losses	47,952	57,352	47,952	57,352
Allowance for loan losses: Individually evaluated	21	55	21	55
Allowance for loan losses: Collectively evaluated	26,707	31,184	26,707	31,184
Reserve for unfunded lending commitments: Collectively evaluated	21,224	26,113	21,224	26,113
Loans: Individually evaluated for impairment	129	1,007	129	1,007
Loans: Collectively evaluated for impairment	1,294,907	1,127,952	1,294,907	1,127,952
Loans receivable	1,295,036	1,128,959	1,295,036	1,128,959	1,065,057
Total Commercial [Member] | Non-Purchased Credit Impaired Loans [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				7,287
Allowance for loan losses: Charge-offs			(231)	(1,501)
Allowance for loan losses: Recoveries				46
Allowance for loan losses: Net provision for loan losses			14,537	71,210
Total Commercial [Member] | Non-Purchased Credit Impaired Loans [Member] | Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				7,478
Allowance for loan losses: Charge-offs			(256)	(5)
Allowance for loan losses: Recoveries			1,164	451
Allowance for loan losses: Net provision for loan losses			(642)	13,965
Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			218,827	117,409
Allowance for loan losses: Cumulative effect of change in accounting principle				6,060
Allowance for loan losses: Ending balance	174,295	206,437	174,295	206,437
Reserve for unfunded lending commitments: Beginning balance			4,910	3,974
Reserve for unfunded lending commitments: Provision for losses			1,101	(2,473)
Reserve for unfunded lending commitments: Ending balance	6,011	7,561	6,011	7,561
Total allowance for credit losses	180,306	213,998	180,306	213,998
Allowance for loan losses: Individually evaluated	3,344	13,856	3,344	13,856
Allowance for loan losses: Collectively evaluated	170,951	192,581	170,951	192,581
Reserve for unfunded lending commitments: Individually evaluated	241	751	241	751
Reserve for unfunded lending commitments: Collectively evaluated	5,770	6,810	5,770	6,810
Loans: Individually evaluated for impairment	20,721	99,296	20,721	99,296
Loans: Collectively evaluated for impairment	12,321,857	13,128,243	12,321,857	13,128,243
Loans receivable	12,342,578	13,227,539	12,342,578	13,227,539	12,844,428
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			149,693	106,432
Allowance for loan losses: Cumulative effect of change in accounting principle				5,772
Allowance for loan losses: Ending balance	112,523	144,971	112,523	144,971
Reserve for unfunded lending commitments: Beginning balance			4,529	3,974
Reserve for unfunded lending commitments: Provision for losses			1,174	(2,900)
Reserve for unfunded lending commitments: Ending balance	5,703	6,846	5,703	6,846
Total allowance for credit losses	118,226	151,817	118,226	151,817
Allowance for loan losses: Individually evaluated	2,675	12,619	2,675	12,619
Allowance for loan losses: Collectively evaluated	109,848	132,352	109,848	132,352
Reserve for unfunded lending commitments: Individually evaluated	241	751	241	751
Reserve for unfunded lending commitments: Collectively evaluated	5,462	6,095	5,462	6,095
Loans: Individually evaluated for impairment	13,642	89,314	13,642	89,314
Loans: Collectively evaluated for impairment	9,519,068	10,375,966	9,519,068	10,375,966
Loans receivable	9,532,710	10,465,280	9,532,710	10,465,280	9,986,983
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			69,134	10,977
Allowance for loan losses: Cumulative effect of change in accounting principle				288
Allowance for loan losses: Ending balance	61,772	61,466	61,772	61,466
Reserve for unfunded lending commitments: Beginning balance			381
Reserve for unfunded lending commitments: Provision for losses			(73)	427
Reserve for unfunded lending commitments: Ending balance	308	715	308	715
Total allowance for credit losses	62,080	62,181	62,080	62,181
Allowance for loan losses: Individually evaluated	669	1,237	669	1,237
Allowance for loan losses: Collectively evaluated	61,103	60,229	61,103	60,229
Reserve for unfunded lending commitments: Collectively evaluated	308	715	308	715
Loans: Individually evaluated for impairment	7,079	9,982	7,079	9,982
Loans: Collectively evaluated for impairment	2,802,789	2,752,277	2,802,789	2,752,277
Loans receivable	2,809,868	2,762,259	2,809,868	2,762,259	2,857,445
Total Commercial [Member] | Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				14,633
Allowance for loan losses: Charge-offs			(30,614)	(341,272)
Allowance for loan losses: Recoveries			4,474	3,406
Allowance for loan losses: Net provision for loan losses			(18,392)	412,261
Total Commercial [Member] | Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				(244)
Allowance for loan losses: Charge-offs			(28,932)	(339,566)
Allowance for loan losses: Recoveries			4,187	3,299
Allowance for loan losses: Net provision for loan losses			(12,425)	375,050
Total Commercial [Member] | Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				14,877
Allowance for loan losses: Charge-offs			(1,682)	(1,706)
Allowance for loan losses: Recoveries			287	107
Allowance for loan losses: Net provision for loan losses			(5,967)	37,211
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			48,842	20,331
Allowance for loan losses: Cumulative effect of change in accounting principle				17
Allowance for loan losses: Ending balance	36,465	57,351	36,465	57,351
Reserve for unfunded lending commitments: Beginning balance			19
Reserve for unfunded lending commitments: Provision for losses			(6)	5
Reserve for unfunded lending commitments: Ending balance	13	22	13	22
Total allowance for credit losses	36,478	57,373	36,478	57,373
Allowance for loan losses: Individually evaluated	437	477	437	477
Allowance for loan losses: Collectively evaluated	36,028	56,874	36,028	56,874
Reserve for unfunded lending commitments: Collectively evaluated	13	22	13	22
Loans: Individually evaluated for impairment	6,347	5,710	6,347	5,710
Loans: Collectively evaluated for impairment	2,406,112	2,871,606	2,406,112	2,871,606
Loans receivable	2,412,459	2,877,316	2,412,459	2,877,316	2,665,212
Residential Mortgages [Member] | Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				12,921
Allowance for loan losses: Charge-offs			(207)	(141)
Allowance for loan losses: Recoveries			437	761
Allowance for loan losses: Net provision for loan losses			(12,607)	23,479
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance			46,572	23,292
Allowance for loan losses: Cumulative effect of change in accounting principle				5,146
Allowance for loan losses: Ending balance	38,400	49,700	38,400	49,700
Reserve for unfunded lending commitments: Beginning balance			1,185
Reserve for unfunded lending commitments: Provision for losses			(252)	(3,369)
Reserve for unfunded lending commitments: Ending balance	933	1,777	933	1,777
Total allowance for credit losses	39,333	51,477	39,333	51,477
Allowance for loan losses: Individually evaluated	204	377	204	377
Allowance for loan losses: Collectively evaluated	38,196	49,323	38,196	49,323
Reserve for unfunded lending commitments: Collectively evaluated	933	1,777	933	1,777
Loans: Individually evaluated for impairment	2,663	3,970	2,663	3,970
Loans: Collectively evaluated for impairment	1,676,766	2,040,294	1,676,766	2,040,294
Loans receivable	$ 1,679,429	$ 2,044,264	1,679,429	2,044,264	$ 1,857,295
Consumer [Member] | Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Cumulative effect of change in accounting principle				7,092
Allowance for loan losses: Charge-offs			(6,618)	(10,736)
Allowance for loan losses: Recoveries			3,099	2,543
Allowance for loan losses: Net provision for loan losses			$ (4,653)	$ 27,509