Premises and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premises and equipment
Total premises and equipment	$ 114,372,000	$ 112,758,000
Accumulated depreciation and amortization	(59,760,000)	(56,050,000)
Net premises and equipment	54,612,000	56,708,000
Long-lived asset impairment charges	410,000	0	$ 150,000
Depreciation and amortization of properties and equipment	5,658,000	5,245,000	$ 4,780,000
Land
Premises and equipment
Total premises and equipment	15,413,000	16,127,000
Buildings and improvements
Premises and equipment
Total premises and equipment	58,981,000	59,027,000
Furniture and equipment
Premises and equipment
Total premises and equipment	$ 39,978,000	$ 37,604,000