Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Stock Repurchase Program, Authorized Amount			$ 250,000,000
Stock Repurchased During Period, Shares			1,400,000.0
Payments for Repurchase of Common Stock			88,500,000	50,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount			161,500,000
Numerator:
Net income	$ 53,100,000	$ 35,100,000	$ 95,200,000	$ 62,200,000
Denominator:
Denominator for basic earnings per share — weighted average shares	45,500,000	46,500,000	45,700,000	46,700,000
Effect of dilutive securities:
Equity compensation plans	800,000	600,000	800,000	700,000
Convertible preferred stock	0		0
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion	46,300,000	47,100,000	46,500,000	47,400,000
Basic earnings per share (in dollars per share)	$ 1.17	$ 0.75	$ 2.08	$ 1.33
Diluted earnings per share (in dollars per share)	$ 1.15	$ 0.74	$ 2.05	$ 1.31