Premises 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 premises and equipment, gross	$ 262,387	$ 272,303
Less accumulated depreciation	(135,491)	(127,291)
Premises and equipment, net	126,896	145,012
Net rent expense under operating leases	6,400	3,300	$ 1,700
Closed branch offices transferred to other assets	13,246	4,846	$ 2,692
Land and land improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	31,427	36,185
Buildings
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	130,028	144,155
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 100,932	$ 91,963