Loans and Allowance for Credit Losses (Allowance for Credit Losses by Portfolio Class) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	$ (26,955)	$ 24,999	(49,095)	578,690
Allowance for loan losses: Ending balance	371,521	448,674	371,521	448,674
Reserve for unfunded lending commitments: Beginning balance			29,907	3,974
Reserve for unfunded lending commitments: Provision for losses			(961)	222
Reserve for unfunded lending commitments: Ending balance	28,946	31,526	28,946	31,526
Total allowance for credit losses	400,467	480,200	400,467	480,200
Allowance for loan losses: Individually evaluated	835	29,713	835	29,713
Allowance for loan losses: Collectively evaluated	370,686	418,961	370,686	418,961
Reserve for unfunded lending commitments: Individually evaluated		997		997
Reserve for unfunded lending commitments: Collectively evaluated	28,946	30,529	28,946	30,529
Loans: Individually evaluated for impairment	22,076	101,637	22,076	101,637
Loans: Collectively evaluated for impairment	20,863,939	22,138,567	20,863,939	22,138,567
Loans receivable	20,886,015	22,240,204	20,886,015	22,240,204	$ 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			(44,681)	(381,979)
Allowance for loan losses: Recoveries			14,159	11,523
Allowance for loan losses: Net provision for loan losses			(48,134)	578,468
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	121,095	104,652	121,095	104,652
Reserve for unfunded lending commitments: Beginning balance			1,099
Reserve for unfunded lending commitments: Provision for losses			124	1,599
Reserve for unfunded lending commitments: Ending balance	1,223	2,048	1,223	2,048
Total allowance for credit losses	122,318	106,700	122,318	106,700
Allowance for loan losses: Individually evaluated	20	24	20	24
Allowance for loan losses: Collectively evaluated	121,075	104,628	121,075	104,628
Reserve for unfunded lending commitments: Collectively evaluated	1,223	2,048	1,223	2,048
Loans: Individually evaluated for impairment	4,004	5,549	4,004	5,549
Loans: Collectively evaluated for impairment	3,463,935	3,401,005	3,463,935	3,401,005
Loans receivable	3,467,939	3,406,554	3,467,939	3,406,554	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	22,576	29,695	22,576	29,695
Reserve for unfunded lending commitments: Beginning balance			22,694
Reserve for unfunded lending commitments: Provision for losses			(383)	6,046
Reserve for unfunded lending commitments: Ending balance	22,311	21,704	22,311	21,704
Total allowance for credit losses	44,887	51,399	44,887	51,399
Allowance for loan losses: Individually evaluated	20	169	20	169
Allowance for loan losses: Collectively evaluated	22,556	29,526	22,556	29,526
Reserve for unfunded lending commitments: Collectively evaluated	22,311	21,704	22,311	21,704
Loans: Individually evaluated for impairment	127	1,837	127	1,837
Loans: Collectively evaluated for impairment	1,213,864	1,094,312	1,213,864	1,094,312
Loans receivable	1,213,991	1,096,149	1,213,991	1,096,149	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)	(2,211)
Allowance for loan losses: Recoveries			100	46
Allowance for loan losses: Net provision for loan losses			11,752	78,661
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			(267)	(7)
Allowance for loan losses: Recoveries			1,548	549
Allowance for loan losses: Net provision for loan losses			(5,167)	12,325
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	163,442	214,072	163,442	214,072
Reserve for unfunded lending commitments: Beginning balance			4,910	3,974
Reserve for unfunded lending commitments: Provision for losses			(307)	(3,599)
Reserve for unfunded lending commitments: Ending balance	4,603	6,435	4,603	6,435
Total allowance for credit losses	168,045	220,507	168,045	220,507
Allowance for loan losses: Individually evaluated	146	28,648	146	28,648
Allowance for loan losses: Collectively evaluated	163,296	185,424	163,296	185,424
Reserve for unfunded lending commitments: Individually evaluated		992		992
Reserve for unfunded lending commitments: Collectively evaluated	4,603	5,443	4,603	5,443
Loans: Individually evaluated for impairment	11,547	84,263	11,547	84,263
Loans: Collectively evaluated for impairment	12,218,369	12,952,932	12,218,369	12,952,932
Loans receivable	12,229,916	13,037,195	12,229,916	13,037,195	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	106,309	148,051	106,309	148,051
Reserve for unfunded lending commitments: Beginning balance			4,529	3,974
Reserve for unfunded lending commitments: Provision for losses			(176)	(3,786)
Reserve for unfunded lending commitments: Ending balance	4,353	5,960	4,353	5,960
Total allowance for credit losses	110,662	154,011	110,662	154,011
Allowance for loan losses: Individually evaluated	113	27,304	113	27,304
Allowance for loan losses: Collectively evaluated	106,196	120,747	106,196	120,747
Reserve for unfunded lending commitments: Individually evaluated		992		992
Reserve for unfunded lending commitments: Collectively evaluated	4,353	4,968	4,353	4,968
Loans: Individually evaluated for impairment	5,929	73,139	5,929	73,139
Loans: Collectively evaluated for impairment	9,411,061	10,184,649	9,411,061	10,184,649
Loans receivable	9,416,990	10,257,788	9,416,990	10,257,788	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	57,133	66,021	57,133	66,021
Reserve for unfunded lending commitments: Beginning balance			381
Reserve for unfunded lending commitments: Provision for losses			(131)	187
Reserve for unfunded lending commitments: Ending balance	250	475	250	475
Total allowance for credit losses	57,383	66,496	57,383	66,496
Allowance for loan losses: Individually evaluated	33	1,344	33	1,344
Allowance for loan losses: Collectively evaluated	57,100	64,677	57,100	64,677
Reserve for unfunded lending commitments: Collectively evaluated	250	475	250	475
Loans: Individually evaluated for impairment	5,618	11,124	5,618	11,124
Loans: Collectively evaluated for impairment	2,807,308	2,768,283	2,807,308	2,768,283
Loans receivable	2,812,926	2,779,407	2,812,926	2,779,407	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			(34,091)	(365,951)
Allowance for loan losses: Recoveries			6,942	5,490
Allowance for loan losses: Net provision for loan losses			(28,236)	442,491
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			(32,369)	(364,123)
Allowance for loan losses: Recoveries			6,579	4,831
Allowance for loan losses: Net provision for loan losses			(17,594)	401,155
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			(1,722)	(1,828)
Allowance for loan losses: Recoveries			363	659
Allowance for loan losses: Net provision for loan losses			(10,642)	41,336
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	31,073	51,773	31,073	51,773
Reserve for unfunded lending commitments: Beginning balance			19
Reserve for unfunded lending commitments: Provision for losses			(8)	(11)
Reserve for unfunded lending commitments: Ending balance	11	6	11	6
Total allowance for credit losses	31,084	51,779	31,084	51,779
Allowance for loan losses: Individually evaluated	447	416	447	416
Allowance for loan losses: Collectively evaluated	30,626	51,357	30,626	51,357
Reserve for unfunded lending commitments: Collectively evaluated	11	6	11	6
Loans: Individually evaluated for impairment	5,083	6,064	5,083	6,064
Loans: Collectively evaluated for impairment	2,345,970	2,748,324	2,345,970	2,748,324
Loans receivable	2,351,053	2,754,388	2,351,053	2,754,388	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			(218)	(170)
Allowance for loan losses: Recoveries			933	1,078
Allowance for loan losses: Net provision for loan losses			(18,484)	17,613
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	33,335	48,482	33,335	48,482
Reserve for unfunded lending commitments: Beginning balance			1,185
Reserve for unfunded lending commitments: Provision for losses			(387)	(3,813)
Reserve for unfunded lending commitments: Ending balance	798	1,333	798	1,333
Total allowance for credit losses	34,133	49,815	34,133	49,815
Allowance for loan losses: Individually evaluated	202	456	202	456
Allowance for loan losses: Collectively evaluated	33,133	48,026	33,133	48,026
Reserve for unfunded lending commitments: Individually evaluated		5		5
Reserve for unfunded lending commitments: Collectively evaluated	798	1,328	798	1,328
Loans: Individually evaluated for impairment	1,315	3,924	1,315	3,924
Loans: Collectively evaluated for impairment	1,621,801	1,941,994	1,621,801	1,941,994
Loans receivable	$ 1,623,116	$ 1,945,918	1,623,116	1,945,918	$ 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			(9,874)	(13,640)
Allowance for loan losses: Recoveries			4,636	4,360
Allowance for loan losses: Net provision for loan losses			$ (7,999)	$ 27,378