Stock-Based Compensation (Details 6) (Stock options, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Minimum
Black-Scholes option valuation model, assumptions
Risk-free interest rate (as a percent)	0.82%	1.08%	1.64%
Volatility factor (as a percent)	40.36%	34.68%	31.00%
Expected term of options	5 years 10 months 24 days	5 years 1 month 6 days	6 years 1 month 6 days
Weighted-average grant-date fair value (in dollars per share)	$ 10.60	$ 8.07	$ 6.44
Maximum
Black-Scholes option valuation model, assumptions
Risk-free interest rate (as a percent)	1.33%	2.57%	2.97%
Volatility factor (as a percent)	41.12%	38.92%	32.73%
Expected term of options	6 years	6 years	6 years 2 months 12 days
Weighted-average grant-date fair value (in dollars per share)	$ 13.70	$ 14.42	$ 9.11