Commitments and Contingent Liabilities - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial instruments with off-balance sheet risk
Contract amount	$ 6,100,000	$ 6,100,000
Commitments to extend credit
Financial instruments with off-balance sheet risk
Contract amount	5,934,535	5,907,690
Standby letters of credit
Financial instruments with off-balance sheet risk
Contract amount	185,108	181,412
Commercial letters of credit
Financial instruments with off-balance sheet risk
Contract amount	$ 3,834	$ 7,334