Earnings Per Share (Details) (USD $)	3 Months Ended		15 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Earnings Per Share [Abstract]
Stock Repurchase Program, Authorized Amount		$ 250,000,000
Stock Repurchased During Period, Shares	500,000.0		2,400,000.0
Treasury Stock, Value, Acquired, Cost Method	27,000,000		151,600,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	98,400,000		98,400,000
Numerator:
Net income	$ 62,200,000	$ 42,100,000
Denominator:
Denominator for basic earnings per share — weighted average shares	44,100,000	46,000,000
Effect of dilutive securities:
Equity compensation plans	700,000	800,000
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion	44,800,000	46,800,000
Basic earnings per share (in dollars per share)	$ 1.41	$ 0.92
Diluted earnings per share (in dollars per share)	$ 1.39	$ 0.90