Mortgage Servicing Rights - Sensitivity Analysis (Details) - MSR - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Sensitivity analysis
Constant prepayment rate: Impact of 10% adverse change	$ (1,962)		$ (1,962)		$ (1,948)
Constant prepayment rate: Impact of 20% adverse change	(3,980)		(3,980)		(3,839)
Discount rate: Impact of 10% adverse change	(2,899)		(2,899)		(2,135)
Discount rate: Impact of 20% adverse change	(5,556)		(5,556)		$ (4,103)
Contractually specified servicing fees, late fees and ancillary fees	$ 5,400	$ 4,200	$ 17,300	$ 15,700