Mortgage Servicing Rights - Schedule of Servicing Income and Expense Included in Mortgage Banking Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing income:
Servicing income	$ 13,168	$ 12,063	$ 3,614
Change in fair value of mortgage servicing rights	(4,023)
Change in fair value of derivative hedging instruments	599
Total servicing income	9,744	12,063	3,614
Servicing expenses:
Servicing asset amortization		8,321	2,601
Servicing asset impairment		4,678	194
Loss on sale of mortgage servicing rights and related hedges and transaction costs on sale	249	4,447
Other servicing expenses	4,896	2,325	633
Total servicing expenses	5,145	19,771	3,428
Net servicing income (loss)	$ 4,599	$ (7,708)	$ 186