Short-term Borrowings - Summary of Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal Funds Purchased
Short-term Debt [Line Items]
Average balance	$ 737,715	$ 405,110	$ 447,137
Year-end balance	548,344	256,567	399,820
Maximum month-end outstanding	$ 1,281,853	$ 503,138	$ 568,490
Average rate for the year	2.08%	1.89%	1.06%
Average rate at year-end	1.55%	2.50%	1.48%
Securities Sold Under Agreements to Repurchase
Short-term Debt [Line Items]
Average balance	$ 701,164	$ 713,841	$ 578,666
Year-end balance	716,925	762,592	656,602
Maximum month-end outstanding	$ 772,092	$ 891,425	$ 743,684
Average rate for the year	1.89%	1.40%	0.72%
Average rate at year-end	1.72%	1.66%	0.64%
Trading Liabilities
Short-term Debt [Line Items]
Average balance	$ 503,302	$ 682,943	$ 685,891
Year-end balance	505,581	335,380	638,515
Maximum month-end outstanding	$ 754,220	$ 890,717	$ 896,943
Average rate for the year	2.48%	2.83%	2.26%
Average rate at year-end	2.07%	3.21%	2.22%
Other Short-term Borrowings
Short-term Debt [Line Items]
Average balance	$ 538,249	$ 1,046,585	$ 554,502
Year-end balance	2,253,045	114,764	2,626,213
Maximum month-end outstanding	$ 2,276,139	$ 2,229,155	$ 2,626,213
Average rate for the year	2.34%	1.82%	1.28%
Average rate at year-end	2.14%	2.48%	1.44%