Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Allowance for loan losses [Roll Forward]
Beginning balance	$ 243,259	$ 201,087	$ 225,524	$ 189,056
Provision for loan losses	7,907	4,782	55,573	9,130
Loans charged off	(8,101)	(5,274)	(40,937)	(10,320)
Recoveries	2,038	3,521	4,943	16,250
Ending balance	245,103	204,116	245,103	204,116
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	9,045	882	1,711	1,230
Provision for off-balance sheet credit losses	2,093	2,718	9,427	2,370
Ending balance	11,138	3,600	11,138	3,600
Total provision for credit losses	10,000	7,500	65,000	11,500
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					$ 16,227,834	$ 15,794,026	$ 15,278,094
Individually measured for impairment, recorded investment					236,952	147,128	89,347
Total					16,464,786	15,941,154	15,367,441
Related allowance [Abstract]
Collectively measured for impairment, related allowance					210,353	179,005	171,419
Individually measured for impairment, related allowance					6,564	16,393	4,951
Total	243,259	201,087	225,524	189,056	245,103	225,524	204,116
Commercial
Allowance for loan losses [Roll Forward]
Beginning balance	145,139	107,037	130,334	90,875
Provision for loan losses	2,420	4,694	45,995	20,869
Loans charged off	(6,266)	(3,497)	(35,747)	(4,552)
Recoveries	177	759	888	1,801
Ending balance	141,470	108,993	141,470	108,993
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	8,752	595	1,506	475
Provision for off-balance sheet credit losses	2,170	1,873	9,416	1,993
Ending balance	10,922	2,468	10,922	2,468
Total provision for credit losses	4,590	6,567	55,411	22,862
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					9,943,699	10,176,107	9,763,624
Individually measured for impairment, recorded investment					176,464	76,424	33,798
Total					10,120,163	10,252,531	9,797,422
Related allowance [Abstract]
Collectively measured for impairment, related allowance					134,968	114,027	104,157
Individually measured for impairment, related allowance					6,502	16,307	4,836
Total	145,139	107,037	130,334	90,875	141,470	130,334	108,993
Commercial real estate
Allowance for loan losses [Roll Forward]
Beginning balance	46,745	39,744	41,391	42,445
Provision for loan losses	2,551	180	7,538	(11,571)
Loans charged off	0	0	0	(44)
Recoveries	521	1,865	888	10,959
Ending balance	49,817	41,789	49,817	41,789
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	203	242	153	707
Provision for off-balance sheet credit losses	(53)	847	(3)	382
Ending balance	150	1,089	150	1,089
Total provision for credit losses	2,498	1,027	7,535	(11,189)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					3,786,248	3,250,032	3,224,111
Individually measured for impairment, recorded investment					7,350	9,001	10,956
Total					3,793,598	3,259,033	3,235,067
Related allowance [Abstract]
Collectively measured for impairment, related allowance					49,817	41,373	41,771
Individually measured for impairment, related allowance					0	18	18
Total	46,745	39,744	41,391	42,445	49,817	41,391	41,789
Residential mortgage
Allowance for loan losses [Roll Forward]
Beginning balance	18,690	21,449	19,509	23,458
Provision for loan losses	(466)	(349)	(829)	(1,938)
Loans charged off	(285)	(446)	(1,104)	(1,784)
Recoveries	650	205	1,013	1,123
Ending balance	18,589	20,859	18,589	20,859
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	62	26	30	28
Provision for off-balance sheet credit losses	(7)	(2)	25	(4)
Ending balance	55	24	55	24
Total provision for credit losses	(473)	(351)	(804)	(1,942)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					1,820,341	1,815,653	1,824,896
Individually measured for impairment, recorded investment					52,452	61,240	44,099
Total					1,872,793	1,876,893	1,868,995
Related allowance [Abstract]
Collectively measured for impairment, related allowance					18,527	19,441	20,762
Individually measured for impairment, related allowance					62	68	97
Total	18,690	21,449	19,509	23,458	18,589	19,509	20,859
Personal
Allowance for loan losses [Roll Forward]
Beginning balance	6,001	3,955	4,164	4,233
Provision for loan losses	1,900	1,413	4,809	2,069
Loans charged off	(1,550)	(1,331)	(4,086)	(3,940)
Recoveries	690	692	2,154	2,367
Ending balance	7,041	4,729	7,041	4,729
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	28	19	22	20
Provision for off-balance sheet credit losses	(17)	0	(11)	(1)
Ending balance	11	19	11	19
Total provision for credit losses	1,883	1,413	4,798	2,068
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					677,546	552,234	465,463
Individually measured for impairment, recorded investment					686	463	494
Total					678,232	552,697	465,957
Related allowance [Abstract]
Collectively measured for impairment, related allowance					7,041	4,164	4,729
Individually measured for impairment, related allowance					0	0	0
Total	6,001	3,955	4,164	4,233	7,041	4,164	4,729
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance			195,398
Ending balance	216,917	176,370	216,917	176,370
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					16,227,834	15,794,026	15,278,094
Individually measured for impairment, recorded investment					236,952	147,128	89,347
Total					16,464,786	15,941,154	15,367,441
Related allowance [Abstract]
Collectively measured for impairment, related allowance					210,353	179,005	171,419
Individually measured for impairment, related allowance					6,564	16,393	4,951
Total	216,917	176,370	195,398	176,370	216,917	195,398	176,370
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	26,684	28,902	30,126	28,045
Provision for loan losses	1,502	(1,156)	(1,940)	(299)
Loans charged off	0	0	0	0
Recoveries	0	0	0	0
Ending balance	28,186	27,746	28,186	27,746
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	1,502	(1,156)	(1,940)	(299)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					0	0	0
Individually measured for impairment, recorded investment					0	0	0
Total					0	0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance					0	0	0
Individually measured for impairment, related allowance					0	0	0
Total	$ 26,684	$ 28,902	$ 30,126	$ 28,045	$ 28,186	$ 30,126	$ 27,746