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Retirement and Share-based Compensation Plans (Defined Contribution Plan) (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Defined contribution plan, maximum annual employee contribution $ 18,000 $ 17,500 $ 17,500
Defined contribution plan, employer plan contributions $ 441,000 $ 423,000 $ 391,000