Commitments, Contingent Liabilities and Guarantees - Off-Balance Sheet Risks (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet risks	$ 8,177,360	$ 2,929,329
Total commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet risks	8,048,168	2,908,667
Standby letters of credit and guarantees on industrial revenue bonds
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet risks	129,192	20,662
Commercial | Total commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet risks	5,743,072	1,280,707
Consumer Loan Portfolio | Total commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet risks	$ 2,305,096	$ 1,627,960