Commitments and Contingent Liabilities - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Commitments to extend credit
Financial instruments with off-balance sheet risk
Contract amount	$ 5,438,176	$ 5,121,811
Standby letters of credit
Financial instruments with off-balance sheet risk
Contract amount	160,515	60,848
Commercial Letters of credit
Financial instruments with off-balance sheet risk
Contract amount	$ 5,853	$ 6,813