Premises, Furniture and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total	$ 267,948	$ 256,453
Less accumulated depreciation	(95,624)	(92,839)
Premises, furniture and equipment, net	172,324	163,614
Depreciation expense	11,100	10,400	$ 8,900
Land and land improvements
Property, Plant and Equipment [Line Items]
Total	48,621	42,802
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Total	155,209	146,628
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total	$ 64,118	$ 67,023