Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Allowance for loan losses [Roll Forward]
Beginning balance	$ 202,534	$ 215,142	$ 207,457	$ 230,682
Provision for loan losses	12,539	4,408	25,426	709
Loans charged off	(11,707)	(11,073)	(36,709)	(29,068)
Recoveries	1,066	2,092	8,258	8,246
Ending balance	204,432	210,569	204,432	210,569
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,903	2,433	1,790	3,734
Provision for off-balance sheet credit losses	(539)	(408)	(426)	(1,709)
Ending balance	1,364	2,025	1,364	2,025
Total provision for credit losses	12,000	4,000	25,000	(1,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					$ 22,112,901	$ 21,493,483
Individually measured for impairment, recorded investment					172,466	163,247
Total					22,285,367	21,656,730
Related allowance [Abstract]
Collectively measured for impairment, related allowance					179,144	180,957
Individually measured for impairment, related allowance					7,533	8,732
Total	204,432	215,142	204,432	210,569	204,432	207,457
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	106,397	113,722	102,226	124,269
Provision for loan losses	9,861	(1,285)	34,740	2,720
Loans charged off	(9,875)	(9,602)	(31,728)	(24,940)
Recoveries	260	1,263	1,405	2,049
Ending balance	106,643	104,098	106,643	104,098
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,742	2,361	1,655	3,644
Provision for off-balance sheet credit losses	(536)	(424)	(449)	(1,707)
Ending balance	1,206	1,937	1,206	1,937
Total provision for credit losses	9,325	(1,709)	34,291	1,013
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					14,312,919	13,536,237
Individually measured for impairment, recorded investment					111,706	99,841
Total					14,424,625	13,636,078
Related allowance [Abstract]
Collectively measured for impairment, related allowance					99,110	93,494
Individually measured for impairment, related allowance					7,533	8,732
Total	106,397	113,722	102,226	104,098	106,643	102,226
Commercial real estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	54,188	58,758	60,026	56,621
Provision for loan losses	102	1,391	(10,075)	248
Loans charged off	0	0	(118)	0
Recoveries	60	40	4,517	3,320
Ending balance	54,350	60,189	54,350	60,189
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	116	17	52	45
Provision for off-balance sheet credit losses	(3)	19	61	(9)
Ending balance	113	36	113	36
Total provision for credit losses	99	1,410	(10,014)	239
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					4,602,872	4,743,192
Individually measured for impairment, recorded investment					23,185	21,621
Total					4,626,057	4,764,813
Related allowance [Abstract]
Collectively measured for impairment, related allowance					54,350	60,026
Individually measured for impairment, related allowance					0	0
Total	54,188	58,758	60,026	56,621	54,350	60,026
Residential mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	15,724	18,544	17,964	18,451
Provision for loan losses	(253)	1	(2,660)	(418)
Loans charged off	(56)	(91)	(192)	(326)
Recoveries	119	229	422	976
Ending balance	15,534	18,683	15,534	18,683
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	44	53	52	43
Provision for off-balance sheet credit losses	0	(3)	(8)	7
Ending balance	44	50	44	50
Total provision for credit losses	(253)	(2)	(2,668)	(411)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					2,079,999	2,188,478
Individually measured for impairment, recorded investment					37,304	41,555
Total					2,117,303	2,230,033
Related allowance [Abstract]
Collectively measured for impairment, related allowance					15,534	17,964
Individually measured for impairment, related allowance					0	0
Total	15,724	18,544	15,534	18,451	15,534	17,964
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	9,388	8,646	9,473	9,124
Provision for loan losses	1,911	883	3,434	1,486
Loans charged off	(1,776)	(1,380)	(4,671)	(3,802)
Recoveries	627	560	1,914	1,901
Ending balance	10,150	8,709	10,150	8,709
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	1	2	31	2
Provision for off-balance sheet credit losses	0	0	(30)	0
Ending balance	1	2	1	2
Total provision for credit losses	1,911	883	3,404	1,486
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					1,117,111	1,025,576
Individually measured for impairment, recorded investment					271	230
Total					1,117,382	1,025,806
Related allowance [Abstract]
Collectively measured for impairment, related allowance					10,150	9,473
Individually measured for impairment, related allowance					0	0
Total	9,388	8,646	10,150	9,124	10,150	9,473
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance			189,689
Ending balance	186,677		186,677
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					22,112,901	21,493,483
Individually measured for impairment, recorded investment					172,466	163,247
Total					22,285,367	21,656,730
Related allowance [Abstract]
Collectively measured for impairment, related allowance					179,144	180,957
Individually measured for impairment, related allowance					7,533	8,732
Total	186,677		186,677		186,677	189,689
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	16,837	15,472	17,768	22,217
Provision for loan losses	918	3,418	(13)	(3,327)
Loans charged off	0	0	0	0
Recoveries	0	0	0	0
Ending balance	17,755	18,890	17,755	18,890
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0	0	0
Provision for off-balance sheet credit losses	0	0	0	0
Ending balance	0	0	0	0
Total provision for credit losses	918	3,418	(13)	(3,327)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					0	0
Individually measured for impairment, recorded investment					0	0
Total					0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance					0	0
Individually measured for impairment, related allowance					0	0
Total	$ 16,837	$ 15,472	$ 17,755	$ 22,217	$ 17,755	$ 17,768