Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Allowance for loan losses [Roll Forward]
Beginning balance	$ 230,682	$ 246,159	$ 225,524
Provision for loan losses	9,944	510	55,467
Loans charged off	(43,583)	(25,599)	(42,588)
Recoveries	10,414	9,612	7,756
Ending balance	207,457	230,682	246,159
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	3,734	11,244	1,711
Provision for off-balance sheet credit risk	(1,944)	(7,510)	9,533
Ending balance	1,790	3,734	11,244
Total provision for credit losses	8,000	(7,000)	65,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				$ 21,493,483	$ 16,965,550
Individually measured for impairment, recorded investment				163,247	187,874
Total				21,656,730	17,153,424
Related allowance [Abstract]
Collectively measured for impairment, related allowance				180,957	199,634
Individually measured for impairment, related allowance				8,732	8,831
Total measured for impairment, related allowance	230,682	246,159	246,159	207,457	230,682
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	124,269	140,213	130,334
Provision for loan losses	12,521	(595)	43,980
Loans charged off	(37,880)	(19,810)	(35,828)
Recoveries	3,316	4,461	1,727
Ending balance	102,226	124,269	140,213
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	3,644	11,063	1,506
Provision for off-balance sheet credit risk	(1,989)	(7,419)	9,557
Ending balance	1,655	3,644	11,063
Total provision for credit losses	10,532	(8,014)	53,537
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				13,536,237	10,596,672
Individually measured for impairment, recorded investment				99,841	137,303
Total				13,636,078	10,733,975
Related allowance [Abstract]
Collectively measured for impairment, related allowance				93,494	115,438
Individually measured for impairment, related allowance				8,732	8,831
Total measured for impairment, related allowance	124,269	124,269	130,334	102,226	124,269
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	56,621	50,749	41,391
Provision for loan losses	(147)	4,008	8,075
Loans charged off	0	(76)	0
Recoveries	3,552	1,940	1,283
Ending balance	60,026	56,621	50,749
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	45	123	153
Provision for off-balance sheet credit risk	7	(78)	(30)
Ending balance	52	45	123
Total provision for credit losses	(140)	3,930	8,045
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				4,743,192	3,477,132
Individually measured for impairment, recorded investment				21,621	2,855
Total				4,764,813	3,479,987
Related allowance [Abstract]
Collectively measured for impairment, related allowance				60,026	56,621
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	56,621	56,621	41,391	60,026	56,621
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	18,451	18,224	19,509
Provision for loan losses	(1,156)	116	(1,972)
Loans charged off	(378)	(649)	(1,312)
Recoveries	1,047	760	1,999
Ending balance	17,964	18,451	18,224
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	43	50	30
Provision for off-balance sheet credit risk	9	(7)	20
Ending balance	52	43	50
Total provision for credit losses	(1,147)	109	(1,952)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				2,188,478	1,926,239
Individually measured for impairment, recorded investment				41,555	47,447
Total				2,230,033	1,973,686
Related allowance [Abstract]
Collectively measured for impairment, related allowance				17,964	18,451
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	18,451	18,451	18,224	17,964	18,451
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	9,124	8,773	4,164
Provision for loan losses	3,175	2,964	7,310
Loans charged off	(5,325)	(5,064)	(5,448)
Recoveries	2,499	2,451	2,747
Ending balance	9,473	9,124	8,773
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	2	8	22
Provision for off-balance sheet credit risk	29	(6)	(14)
Ending balance	31	2	8
Total provision for credit losses	3,204	2,958	7,296
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				1,025,576	965,507
Individually measured for impairment, recorded investment				230	269
Total				1,025,806	965,776
Related allowance [Abstract]
Collectively measured for impairment, related allowance				9,473	9,124
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	9,473	8,773	8,773	9,473	9,124
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	208,465
Ending balance	189,689	208,465
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				21,493,483	16,965,550
Individually measured for impairment, recorded investment				163,247	187,874
Total				21,656,730	17,153,424
Related allowance [Abstract]
Collectively measured for impairment, related allowance				180,957	199,634
Individually measured for impairment, related allowance				8,732	8,831
Total measured for impairment, related allowance	189,689	208,465		189,689	208,465
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	22,217	28,200	30,126
Provision for loan losses	(4,449)	(5,983)	(1,926)
Loans charged off	0	0	0
Recoveries	0	0	0
Ending balance	17,768	22,217	28,200
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	(4,449)	(5,983)	(1,926)
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	$ 17,768	$ 28,200	$ 30,126	$ 17,768	$ 22,217