Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan losses [Roll Forward]
Beginning balance	$ 225,524	$ 189,056	$ 185,396
Provision for loan losses	55,467	33,519	858
Loans charged off	(42,588)	(15,171)	(16,232)
Recoveries	7,756	18,120	19,034
Ending balance	246,159	225,524	189,056
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,711	1,230	2,088
Provision for off-balance sheet credit risk	9,533	481	(858)
Ending balance	11,244	1,711	1,230
Total provision for credit losses	65,000	34,000	0
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				$ 16,758,676	$ 15,794,026
Individually measured for impairment, recorded investment				230,984	147,128
Total				16,989,660	15,941,154
Related allowance [Abstract]
Collectively measured for impairment, related allowance				217,116	179,005
Individually measured for impairment, related allowance				843	16,393
Total measured for impairment, related allowance	225,524	189,056	185,396	246,159	225,524
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	130,334	90,875	79,180
Provision for loan losses	43,980	43,464	9,561
Loans charged off	(35,828)	(6,734)	(3,569)
Recoveries	1,727	2,729	5,703
Ending balance	140,213	130,334	90,875
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,506	475	119
Provision for off-balance sheet credit risk	9,557	1,031	356
Ending balance	11,063	1,506	475
Total provision for credit losses	53,537	44,495	9,917
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				10,211,871	10,176,107
Individually measured for impairment, recorded investment				178,953	76,424
Total				10,390,824	10,252,531
Related allowance [Abstract]
Collectively measured for impairment, related allowance				139,416	114,027
Individually measured for impairment, related allowance				797	16,307
Total measured for impairment, related allowance	130,334	90,875	79,180	140,213	130,334
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	41,391	42,445	41,573
Provision for loan losses	8,075	(11,189)	(4,084)
Loans charged off	0	(944)	(2,047)
Recoveries	1,283	11,079	7,003
Ending balance	50,749	41,391	42,445
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	153	707	1,876
Provision for off-balance sheet credit risk	(30)	(554)	(1,169)
Ending balance	123	153	707
Total provision for credit losses	8,045	(11,743)	(5,253)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				3,803,525	3,250,032
Individually measured for impairment, recorded investment				5,521	9,001
Total				3,809,046	3,259,033
Related allowance [Abstract]
Collectively measured for impairment, related allowance				50,749	41,373
Individually measured for impairment, related allowance				0	18
Total measured for impairment, related allowance	41,391	42,445	41,573	50,749	41,391
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	19,509	23,458	29,465
Provision for loan losses	(1,972)	(3,004)	(3,559)
Loans charged off	(1,312)	(2,205)	(4,448)
Recoveries	1,999	1,260	2,000
Ending balance	18,224	19,509	23,458
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	30	28	90
Provision for off-balance sheet credit risk	20	2	(62)
Ending balance	50	30	28
Total provision for credit losses	(1,952)	(3,002)	(3,621)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				1,903,612	1,815,653
Individually measured for impairment, recorded investment				46,220	61,240
Total				1,949,832	1,876,893
Related allowance [Abstract]
Collectively measured for impairment, related allowance				18,178	19,441
Individually measured for impairment, related allowance				46	68
Total measured for impairment, related allowance	19,509	23,458	29,465	18,224	19,509
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	4,164	4,233	6,965
Provision for loan losses	7,310	2,167	(892)
Loans charged off	(5,448)	(5,288)	(6,168)
Recoveries	2,747	3,052	4,328
Ending balance	8,773	4,164	4,233
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	22	20	3
Provision for off-balance sheet credit risk	(14)	2	17
Ending balance	8	22	20
Total provision for credit losses	7,296	2,169	(875)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				839,668	552,234
Individually measured for impairment, recorded investment				290	463
Total				839,958	552,697
Related allowance [Abstract]
Collectively measured for impairment, related allowance				8,773	4,164
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	4,164	4,233	6,965	8,773	4,164
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	195,398
Ending balance	217,959	195,398
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				16,758,676	15,794,026
Individually measured for impairment, recorded investment				230,984	147,128
Total				16,989,660	15,941,154
Related allowance [Abstract]
Collectively measured for impairment, related allowance				217,116	179,005
Individually measured for impairment, related allowance				843	16,393
Total measured for impairment, related allowance	195,398	195,398		217,959	195,398
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	30,126	28,045	28,213
Provision for loan losses	(1,926)	2,081	(168)
Loans charged off	0	0	0
Recoveries	0	0	0
Ending balance	28,200	30,126	28,045
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0	0
Provision for off-balance sheet credit risk	0	0	0
Ending balance	0	0	0
Total provision for credit losses	(1,926)	2,081	(168)
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 measured for impairment, related allowance	$ 30,126	$ 28,045	$ 28,213	$ 28,200	$ 30,126