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Summary of Significant Accounting Policies (Details 6) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule Of Share Based Payment Award Stock Options Valuation Assumptions [Abstract]      
Number of stock options granted 307,176 142,908 175,632
Weighted average grant date fair value of stock options granted $ 5.01 $ 11.18 $ 9.01
Weighted average assumptions:      
Risk-free interest rate 1.30% 1.70% 1.90%
Expected dividend yield 3.20% 2.60% 2.50%
Expected life, in years 4 years 10 months 24 days 7 years 2 months 12 days 5 years 8 months 12 days
Expected volatility (based on historical volatility) 25.60% 42.80% 40.30%