Transfers of Financial Assets Servicing Assets at Amortized Cost Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Beginning balance	$ 24,466	$ 20,698	$ 19,379
Additions	9,249	11,312	8,027
Amortization	(8,576)	(7,544)	(6,708)
Ending balance	$ 25,139	$ 24,466	$ 20,698