Commitments and Contingent Liabilities - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial instruments with off-balance sheet risk
Contract amount	$ 5,800,000	$ 5,600,000
Commitments to extend credit
Financial instruments with off-balance sheet risk
Contract amount	5,549,591	5,401,763
Standby letters of credit
Financial instruments with off-balance sheet risk
Contract amount	204,324	161,798
Commercial Letters of credit
Financial instruments with off-balance sheet risk
Contract amount	$ 7,535	$ 5,540