Consolidated Statement of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income
Loans and leases, including fees	$ 3,975,053	$ 4,442,182	$ 4,164,561
Investment securities
Fully taxable	176,469	288,532	323,912
Exempt from federal taxes	183	321	665
Deposits at banks	32,956	141,397	108,182
Other	8,051	7,161	1,391
Total interest income	4,192,712	4,879,593	4,598,711
Interest expense
Savings and interest-checking deposits	146,701	368,003	215,411
Time deposits	66,280	95,426	51,423
Deposits at Cayman Islands office	4,054	21,917	5,633
Short-term borrowings	28	24,741	5,386
Long-term borrowings	109,332	239,242	248,556
Total interest expense	326,395	749,329	526,409
Net interest income	3,866,317	4,130,264	4,072,302
Provision for credit losses	800,000	176,000	132,000
Net interest income after provision for credit losses	3,066,317	3,954,264	3,940,302
Other income
Brokerage services income	47,428	48,922	51,069
Trading account and foreign exchange gains	40,536	62,044	32,547
Gain (loss) on bank investment securities	(9,421)	18,037	(6,301)
Other revenues from operations	470,588	469,320	451,321
Total other income	2,088,444	2,061,679	1,856,000
Other expense
Salaries and employee benefits	1,950,692	1,900,797	1,752,264
Equipment and net occupancy	322,037	324,079	298,828
Outside data processing and software	258,480	229,731	199,025
FDIC assessments	53,803	41,535	68,526
Advertising and marketing	61,904	93,472	85,710
Printing, postage and supplies	39,869	39,893	35,658
Amortization of core deposit and other intangible assets	14,869	19,490	24,522
Other costs of operations	683,586	819,685	823,529
Total other expense	3,385,240	3,468,682	3,288,062
Income before taxes	1,769,521	2,547,261	2,508,240
Income taxes	416,369	618,112	590,160
Net income	1,353,152	1,929,149	1,918,080
Net income available to common shareholders
Basic	1,279,066	1,849,509	1,836,028
Diluted	$ 1,279,068	$ 1,849,511	$ 1,836,035
Net income per common share
Basic	$ 9.94	$ 13.76	$ 12.75
Diluted	$ 9.94	$ 13.75	$ 12.74
Mortgage Banking Revenues [Member]
Other income
Revenue from contract with customer	$ 566,641	$ 457,770	$ 360,442
Service Charges on Deposit Accounts [Member]
Other income
Revenue from contract with customer	370,788	432,978	429,337
Trust Income [Member]
Other income
Revenue from contract with customer	$ 601,884	$ 572,608	$ 537,585