Borrowed Funds - Short-Term Credit Lines Available for Use (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
FRBs Discount Window Primary Credit Program
Line of Credit Facility [Line Items]
Amount outstanding	$ 881,113	$ 843,618
Available federal funds lines
Line of Credit Facility [Line Items]
Amount outstanding	684,000	667,000
Correspondent bank line of credit
Line of Credit Facility [Line Items]
Amount outstanding	$ 50,000	$ 50,000