Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Allowance for loan losses [Roll Forward]
Beginning balance	$ 201,087	$ 190,690	$ 189,056	$ 185,396
Provision for loan losses	4,782	78	9,130	858
Loans charged off	(5,274)	(2,638)	(10,320)	(9,008)
Recoveries	3,521	3,114	16,250	13,998
Ending balance	204,116	191,244	204,116	191,244
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	882	1,308	1,230	2,088
Provision for off-balance sheet credit losses	2,718	(78)	2,370	(858)
Ending balance	3,600	1,230	3,600	1,230
Total provision for credit losses	7,500	0	11,500	0
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					$ 15,278,094	$ 14,127,266	$ 13,587,188
Individually measured for impairment, recorded investment					89,347	80,771	96,551
Total					15,367,441	14,208,037	13,683,739
Related allowance [Abstract]
Collectively measured for impairment, related allowance					171,419	160,699	159,952
Individually measured for impairment, related allowance					4,951	312	3,348
Total measured for impairment, related allowance	201,087	190,690	189,056	185,396	204,116	189,056	191,244
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	107,037	87,806	90,875	79,180
Provision for loan losses	4,694	(1,174)	20,869	4,444
Loans charged off	(3,497)	(117)	(4,552)	(290)
Recoveries	759	260	1,801	3,441
Ending balance	108,993	86,775	108,993	86,775
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	595	345	475	119
Provision for off-balance sheet credit losses	1,873	(65)	1,993	161
Ending balance	2,468	280	2,468	280
Total provision for credit losses	6,567	(1,239)	22,862	4,605
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					9,763,624	9,082,143	8,555,634
Individually measured for impairment, recorded investment					33,798	13,527	16,404
Total					9,797,422	9,095,670	8,572,038
Related allowance [Abstract]
Collectively measured for impairment, related allowance					104,157	90,709	83,609
Individually measured for impairment, related allowance					4,836	166	3,166
Total measured for impairment, related allowance	107,037	87,806	90,875	79,180	108,993	90,875	86,775
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	39,744	41,252	42,445	41,573
Provision for loan losses	180	(84)	(11,571)	(4,633)
Loans charged off	0	(145)	(44)	(365)
Recoveries	1,865	1,410	10,959	5,858
Ending balance	41,789	42,433	41,789	42,433
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	242	902	707	1,876
Provision for off-balance sheet credit losses	847	10	382	(964)
Ending balance	1,089	912	1,089	912
Total provision for credit losses	1,027	(74)	(11,189)	(5,597)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					3,224,111	2,709,593	2,693,539
Individually measured for impairment, recorded investment					10,956	18,557	30,660
Total					3,235,067	2,728,150	2,724,199
Related allowance [Abstract]
Collectively measured for impairment, related allowance					41,771	42,404	42,358
Individually measured for impairment, related allowance					18	41	75
Total measured for impairment, related allowance	39,744	41,252	42,445	41,573	41,789	42,445	42,433
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	21,449	27,654	23,458	29,465
Provision for loan losses	(349)	185	(1,938)	136
Loans charged off	(446)	(773)	(1,784)	(3,611)
Recoveries	205	150	1,123	1,226
Ending balance	20,859	27,216	20,859	27,216
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	26	43	28	90
Provision for off-balance sheet credit losses	(2)	(19)	(4)	(66)
Ending balance	24	24	24	24
Total provision for credit losses	(351)	166	(1,942)	70
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					1,824,896	1,901,391	1,930,756
Individually measured for impairment, recorded investment					44,099	48,121	48,907
Total					1,868,995	1,949,512	1,979,663
Related allowance [Abstract]
Collectively measured for impairment, related allowance					20,762	23,353	27,109
Individually measured for impairment, related allowance					97	105	107
Total measured for impairment, related allowance	21,449	27,654	23,458	29,465	20,859	23,458	27,216
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	3,955	7,029	4,233	6,965
Provision for loan losses	1,413	156	2,069	1,180
Loans charged off	(1,331)	(1,603)	(3,940)	(4,742)
Recoveries	692	1,294	2,367	3,473
Ending balance	4,729	6,876	4,729	6,876
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	19	18	20	3
Provision for off-balance sheet credit losses	0	(4)	(1)	11
Ending balance	19	14	19	14
Total provision for credit losses	1,413	152	2,068	1,191
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					465,463	434,139	407,259
Individually measured for impairment, recorded investment					494	566	580
Total					465,957	434,705	407,839
Related allowance [Abstract]
Collectively measured for impairment, related allowance					4,729	4,233	6,876
Individually measured for impairment, related allowance					0	0	0
Total measured for impairment, related allowance	3,955	7,029	4,233	6,965	4,729	4,233	6,876
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance			161,011
Ending balance	176,370	163,300	176,370	163,300
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					15,278,094	14,127,266	13,587,188
Individually measured for impairment, recorded investment					89,347	80,771	96,551
Total					15,367,441	14,208,037	13,683,739
Related allowance [Abstract]
Collectively measured for impairment, related allowance					171,419	160,699	159,952
Individually measured for impairment, related allowance					4,951	312	3,348
Total measured for impairment, related allowance	176,370	163,300	161,011	163,300	176,370	161,011	163,300
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	28,902	26,949	28,045	28,213
Provision for loan losses	(1,156)	995	(299)	(269)
Loans charged off	0	0	0	0
Recoveries	0	0	0	0
Ending balance	27,746	27,944	27,746	27,944
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	(1,156)	995	(299)	(269)
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 measured for impairment, related allowance	$ 28,902	$ 26,949	$ 28,045	$ 28,213	$ 27,746	$ 28,045	$ 27,944