Stock-Based Compensation (Additional Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-Based Compensation
Proceeds from exercise of stock options	$ 11,220,000	$ 13,058,000	$ 7,635,000
Stock Option
Stock-Based Compensation
Aggregate intrinsic value of stock options exercised	15,100,000	15,000,000	8,100,000
Proceeds from exercise of stock options	11,220,000	13,058,000	7,900,000
Fair value of options that vested	9,000,000	17,400,000	21,600,000
Tax benefit realized on exercise of stock options	$ 888,000	$ 500,000	$ 300,000