Stock-based Compensation Stock-based Compensation (Details textual) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation [Abstract]
Unrecognized stock-based compensation costs, net of estimated forfeitures	$ 32.8
Weighted average period of unrecognized stock-based compensation costs, net of estimated forfeitures	1 year 8 months 12 days
Cash received from the exercise of stock options	8.9	1.2
Related tax benefit realized from the exercise of the stock options	$ 2.7	$ 0.3
Time-vested restricted stock unit [Member]
Statement [Line Items]
Restricted stock units granted	5,600	1,200
Weighted average grant date fair value per share	$ 30.27	$ 25.62
Market-based restricted stock unit
Statement [Line Items]
Restricted stock units granted		7,000
Weighted average grant date fair value per share		$ 15.87
Employee Stock Purchase Plan [Member]
Statement [Line Items]
Number of common stock shares issued	0
Employee Stock
Statement [Line Items]
Shares of common stock reserved for future issuance under all of the stock incentive plans	3,630,000