Certain Transfers of Financial Assets - Carrying Value of Servicing Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Assets at Fair Value [Line Items]
Servicing rights, net	$ 112,615	$ 99,295
Residential mortgage
Servicing Assets at Fair Value [Line Items]
Servicing rights, net	100,679	86,131	$ 72,766
SBA servicing rights
Servicing Assets at Fair Value [Line Items]
Servicing rights, net	4,818	5,707
Indirect automobile loan servicing rights
Servicing Assets at Fair Value [Line Items]
Servicing rights, net	$ 7,118	$ 7,457