Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employees' Stock Ownership Plan
Number of allocated shares acquired prior to December 31, 1992	479,755	543,471
Associated fair values of allocated shares acquired prior to December 31, 1992	$ 3,100,000	$ 3,200,000
Shares
Allocated shares	171,988	192,171
Fair Value
Allocated shares, Fair Value	1,100,000	1,100,000
Profit Sharing Plan
Vesting period	5 years
Expenses related to employee benefit plans
Employee benefits	2,636,000	2,975,000	3,024,000
Interest on employee stock ownership plan debt			5,000
Total employer contributions	2,636,000	2,975,000	3,029,000
Deferred compensation plans for deferral of performance bonuses
Deferred compensation expense	300,000	200,000	200,000
Deferred compensation liability	$ 5,100,000	$ 4,800,000	$ 4,500,000