Commitments and Contingent Liabilities - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial instruments with off-balance sheet risk
Contract amount	$ 6,300,000	$ 6,100,000
Commitments to extend credit
Financial instruments with off-balance sheet risk
Contract amount	6,067,465	5,934,535
Standby letters of credit
Financial instruments with off-balance sheet risk
Contract amount	180,909	185,108
Commercial letters of credit
Financial instruments with off-balance sheet risk
Contract amount	$ 5,014	$ 3,834