Premises and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment
Premises and equipment, gross	$ 303,154	$ 291,191
Less accumulated depreciation	(115,589)	(106,420)
Premises and equipment, net	187,565	184,771
Land
Property, Plant and Equipment
Premises and equipment, gross	38,917	38,743
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	195,549	188,509
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 68,688	$ 63,939