Commitments and Contingencies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Loss Contingencies [Line Items]
Carrying amount included in other assets	$ 83,736,000	$ 60,068,000
Amount of future funding commitments included in carrying amount	47,123,000	39,994,000
Short-term construction loans and letter of credit commitments	1,585,000	7,180,000
Funded portion of short-term loans and letters of credit	5,595,000	0
Contractual amount net of risk participations	46,000,000
Guarantor obligations, advanced payment to merchant	22,900,000
Minimum
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments			$ 0
Maximum
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments			$ 5,000,000
Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	10,153,558,000	9,080,108,000
Guarantor obligations, monetary amount	68,990,000,000	62,080,000,000
Letters of credit
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	157,675,000	153,372,000
Commitments to fund commercial and industrial loans
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	5,527,017,000	5,090,827,000
Commitments to fund commercial real estate, construction, and land development loans
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	2,034,223,000	1,567,583,000
Commitments under home equity lines of credit
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	1,258,657,000	1,137,714,000
Unused credit card lines
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	775,003,000	779,254,000
Other loan commitments
Loss Contingencies [Line Items]
Total letters of credit and unfunded lending commitments	$ 400,983,000	$ 351,358,000