Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 272,737	$ 262,387
Less accumulated depreciation	(149,295)	(135,491)
Premises and equipment, net	123,442	126,896
Net rent expense under operating leases	7,700	6,400	$ 3,300
Closed branch offices transferred to other assets	0	13,246	$ 4,846
Land and land improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	31,357	31,427
Buildings
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	133,720	130,028
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 107,660	$ 100,932