Fair Value - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Average capitalization rate	7.60%
Specific reserve for impaired loans	$ 33,865	$ 28,924	$ 27,122	$ 26,232	$ 26,000	$ 23,400
Additions	8,200
Paydowns and chargeoffs	3,900
Additions to level 3 from foreclosed loans	300
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of impaired loans	7,300		4,200
Specific reserve for impaired loans	6,100		$ 2,400
Increase to level 3 from migrated branches taken out of service	2,000
Reductions related to sale of loans	$ 5,300