Mortgage Servicing Rights - Loans, Fees, Amortization and Carrying Value (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Other Intangible Assets
Unpaid principal amount of consumer loans serviced for others	$ 2,800,000		$ 2,800,000		$ 2,300,000
Contractually specified fees, late charges, and ancillary fees	1,900	$ 1,700	3,600	$ 3,400
Amortization of mortgage servicing rights	1,020	924	2,008	1,936
MSRs
Other Intangible Assets
Amortization of mortgage servicing rights	1,000	$ 900	2,000	$ 1,900
Estimated future amortization expense
Under one year	2,469		2,469
One to two years	2,183		2,183
Two to three years	1,932		1,932
Three to four years	1,707		1,707
Four to five years	1,508		1,508
Details of mortgage servicing rights
Gross carrying amount	63,043		63,043		56,571
Less: accumulated amortization	45,383		45,383		43,375
Net carrying value	$ 17,660		$ 17,660		$ 13,196