Mortgage Servicing Rights - Loans, Fees, Amortization and Carrying Value (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Other Intangible Assets
Unpaid principal amount of consumer loans serviced for others	$ 2,900,000		$ 2,300,000
Contractually specified fees, late charges, and ancillary fees	1,700	$ 1,700
Amortization of mortgage servicing rights	988	$ 1,012
MSRs
Estimated future amortization expense
Under one year	2,593
One to two years	2,296
Two to three years	2,034
Three to four years	1,799
Four to five years	1,591
Details of mortgage servicing rights
Gross carrying amount	63,022		56,571
Less: accumulated amortization	44,363		43,375
Net carrying value	$ 18,659		$ 13,196