Summary of Significant Accounting Policies (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair value of options granted was estimated on the dates of grant using weighted-average assumptions
Number of options granted	175,632	245,424	296,188
Weighted average grant date fair value of options granted	$ 9.01	$ 8.25	$ 6.02
Weighted average assumptions:
Risk-free interest rate	1.90%	1.00%	1.00%
Expected dividend yield	2.50%	2.70%	2.20%
Expected life, in years	5 years 8 months 12 days	5 years 9 months 18 days	5 years 9 months 18 days
Expected volatility (based on historical volatility)	40.30%	54.50%	45.10%