Summary of Significant Accounting Policies (Details 5)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of fair value of option granted
Expected term (in years)	5 years	5 years	5 years 2 months 12 days
Expected volatility	52.10%	51.60%	51.20%
Expected dividend yields	3.20%	3.40%	3.80%
Risk-free interest rates	0.80%	2.00%	2.20%