Mortgage Servicing Rights - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Transfers And Servicing [Abstract]
Mortgage servicing rights sold	$ 39,428,000	$ 39,428,000	$ 11,935,000
Mortgage loans serviced	3,181,483,000	3,181,483,000	1,086,465,000
Mortgage loans serviced related to bulk sale of mortgage servicing rights	$ 0	$ 0		$ 0
Recognized loss on sale of mortgage servicing rights			$ 249,000