Commitments and Contingent Liabilities - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial instruments with off-balance sheet risk
Contract amount	$ 6,200,000	$ 6,100,000
Commitments to extend credit
Financial instruments with off-balance sheet risk
Contract amount	6,060,807	5,907,690
Standby letters of credit
Financial instruments with off-balance sheet risk
Contract amount	180,910	181,412
Commercial Letters of credit
Financial instruments with off-balance sheet risk
Contract amount	$ 4,113	$ 7,334