Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assumptions in Black-Scholes valuation models
Risk-free interest rates, Minimum	0.33%	0.86%	0.80%
Risk-free interest rates, Maximum	0.83%	2.30%	2.65%
Dividend yields
Volatility factor of expected market price, Minimum	0.53%	0.732%	0.795%
Volatility factor of expected market price, Maximum	0.71%	0.797%	1.036%
Forfeiture rate
Maximum [Member]
Assumptions in Black-Scholes valuation models
Weighted-average expected term of option	5 years	5 years	4 years 10 months 24 days
Minimum [Member]
Assumptions in Black-Scholes valuation models
Weighted-average expected term of option	3 years 9 months 18 days	3 years 8 months 12 days	3 years 10 months 24 days