Mortgage Servicing Rights - Schedule of Servicing Income and Expense Included in Mortgage Banking Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Servicing income:
Servicing income	$ 5,576	$ 3,463	$ 15,973	$ 8,958
Change in fair value of mortgage servicing rights	(1,872)	(1,383)	1,656	(3,724)
Change in fair value of mortgage servicing rights hedging instruments	(829)	490	(7,848)	490
Gross servicing income	2,875	2,570	9,781	5,724
Servicing expense:
Loss on sale of mortgage servicing rights				249
Direct servicing expenses	2,114	1,043	5,987	3,181
Gross servicing expense	2,114	1,043	5,987	3,430
Net servicing income	$ 761	$ 1,527	$ 3,794	$ 2,294