Fair Value Measurements - Reconciliation of Assets with Unobservable Inputs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 5,294	$ 3,168
Change included in earnings	(1,613)	(2,589)
Purchases and issuances	18,230	23,641
Sales and settlements	(13,733)	(18,926)
Ending balance	8,178	5,294
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4,157	1,654
Change included in earnings	2	(526)
Purchases and issuances	3,146	3,029
Sales and settlements	0	0
Ending balance	7,305	4,157
Interest rate lock commitments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,137	1,514
Change included in earnings	(1,615)	(2,063)
Purchases and issuances	15,084	20,612
Sales and settlements	(13,733)	(18,926)
Ending balance	$ 873	$ 1,137