Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Allowance for loan losses [Roll Forward]
Beginning balance	$ 233,156	$ 197,686	$ 225,524	$ 189,056
Provision for loan losses	17,562	4,072	47,666	4,348
Loans charged off	(8,845)	(2,877)	(32,836)	(5,046)
Recoveries	1,386	2,206	2,905	12,729
Ending balance	243,259	201,087	243,259	201,087
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	6,607	954	1,711	1,230
Provision for off-balance sheet credit losses	2,438	(72)	7,334	(348)
Ending balance	9,045	882	9,045	882
Total provision for credit losses	20,000	4,000	55,000	4,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					$ 16,159,565	$ 15,794,026	$ 15,033,245
Individually measured for impairment, recorded investment					247,184	147,128	90,891
Total					16,406,749	15,941,154	15,124,136
Related allowance [Abstract]
Collectively measured for impairment, related allowance					212,265	179,005	171,720
Individually measured for impairment, related allowance					4,310	16,393	465
Total measured for impairment, related allowance	233,156	197,686	225,524	189,056	243,259	225,524	201,087
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	139,793	101,411	130,334	90,875
Provision for loan losses	12,478	5,822	43,575	16,175
Loans charged off	(7,355)	(881)	(29,481)	(1,055)
Recoveries	223	685	711	1,042
Ending balance	145,139	107,037	145,139	107,037
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	6,319	577	1,506	475
Provision for off-balance sheet credit losses	2,433	18	7,246	120
Ending balance	8,752	595	8,752	595
Total provision for credit losses	14,911	5,840	50,821	16,295
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					10,174,448	10,176,107	9,751,488
Individually measured for impairment, recorded investment					181,989	76,424	24,233
Total					10,356,437	10,252,531	9,775,721
Related allowance [Abstract]
Collectively measured for impairment, related allowance					140,911	114,027	106,690
Individually measured for impairment, related allowance					4,228	16,307	347
Total measured for impairment, related allowance	139,793	101,411	130,334	90,875	145,139	130,334	107,037
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	44,453	40,819	41,391	42,445
Provision for loan losses	2,010	(1,334)	4,987	(11,751)
Loans charged off	0	(16)	0	(44)
Recoveries	282	275	367	9,094
Ending balance	46,745	39,744	46,745	39,744
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	228	333	153	707
Provision for off-balance sheet credit losses	(25)	(91)	50	(465)
Ending balance	203	242	203	242
Total provision for credit losses	1,985	(1,425)	5,037	(12,216)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					3,574,186	3,250,032	3,013,358
Individually measured for impairment, recorded investment					7,780	9,001	20,139
Total					3,581,966	3,259,033	3,033,497
Related allowance [Abstract]
Collectively measured for impairment, related allowance					46,727	41,373	39,726
Individually measured for impairment, related allowance					18	18	18
Total measured for impairment, related allowance	44,453	40,819	41,391	42,445	46,745	41,391	39,744
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	18,467	23,244	19,509	23,458
Provision for loan losses	368	(1,562)	(363)	(1,589)
Loans charged off	(345)	(714)	(819)	(1,338)
Recoveries	200	481	363	918
Ending balance	18,690	21,449	18,690	21,449
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	58	24	30	28
Provision for off-balance sheet credit losses	4	2	32	(2)
Ending balance	62	26	62	26
Total provision for credit losses	372	(1,560)	(331)	(1,591)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					1,823,862	1,815,653	1,838,759
Individually measured for impairment, recorded investment					57,061	61,240	45,969
Total					1,880,923	1,876,893	1,884,728
Related allowance [Abstract]
Collectively measured for impairment, related allowance					18,626	19,441	21,349
Individually measured for impairment, related allowance					64	68	100
Total measured for impairment, related allowance	18,467	23,244	19,509	23,458	18,690	19,509	21,449
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	5,022	4,139	4,164	4,233
Provision for loan losses	1,443	317	2,909	656
Loans charged off	(1,145)	(1,266)	(2,536)	(2,609)
Recoveries	681	765	1,464	1,675
Ending balance	6,001	3,955	6,001	3,955
Allowance for off-balance sheet credit losses [Roll Forward]
Beginning balance	2	20	22	20
Provision for off-balance sheet credit losses	26	(1)	6	(1)
Ending balance	28	19	28	19
Total provision for credit losses	1,469	316	2,915	655
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					587,069	552,234	429,640
Individually measured for impairment, recorded investment					354	463	550
Total					587,423	552,697	430,190
Related allowance [Abstract]
Collectively measured for impairment, related allowance					6,001	4,164	3,955
Individually measured for impairment, related allowance					0	0	0
Total measured for impairment, related allowance	5,022	4,139	4,164	4,233	6,001	4,164	3,955
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance			195,398
Ending balance	216,575	172,185	216,575	172,185
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment					16,159,565	15,794,026	15,033,245
Individually measured for impairment, recorded investment					247,184	147,128	90,891
Total					16,406,749	15,941,154	15,124,136
Related allowance [Abstract]
Collectively measured for impairment, related allowance					212,265	179,005	171,720
Individually measured for impairment, related allowance					4,310	16,393	465
Total measured for impairment, related allowance	216,575	172,185	195,398	172,185	216,575	195,398	172,185
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	25,421	28,073	30,126	28,045
Provision for loan losses	1,263	829	(3,442)	857
Loans charged off	0	0	0	0
Recoveries	0	0	0	0
Ending balance	26,684	28,902	26,684	28,902
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	1,263	829	(3,442)	857
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	$ 25,421	$ 28,073	$ 30,126	$ 28,045	$ 26,684	$ 30,126	$ 28,902