Premises and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Premises and Equipment
Total, at cost	$ 290,819,000	$ 275,206,000
Less accumulated depreciation and amortization	(144,680,000)	(136,382,000)
Premises and equipment, net	146,139,000	138,824,000
Depreciation and amortization expense	11,900,000	11,500,000	11,700,000
Land and land improvements
Premises and Equipment
Total, at cost	20,041,000	17,308,000
Office buildings and improvements
Premises and Equipment
Total, at cost	152,428,000	139,167,000
Furniture, fixtures and equipment
Premises and Equipment
Total, at cost	106,139,000	106,433,000
Leasehold improvements
Premises and Equipment
Total, at cost	$ 12,211,000	$ 12,298,000