Earnings Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jan. 29, 2016	Jun. 30, 2014
Earnings Per Share [Abstract]
Stock Repurchase Program, Authorized Amount					$ 300,000,000	$ 250,000,000
Stock Repurchased During Period, Shares			1,600,000.0
Treasury Stock, Value, Acquired, Cost Method			$ 70,000,000
Numerator:
Net income	$ 61,200,000	$ 45,400,000	$ 130,500,000	$ 107,600,000
Denominator:
Denominator for basic earnings per share — weighted average shares	40,600,000	43,500,000	41,100,000	43,800,000
Effect of dilutive securities:
Equity compensation plans	500,000	700,000	400,000	700,000
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion	41,100,000	44,200,000	41,500,000	44,500,000
Basic earnings per share (in dollars per share)	$ 1.51	$ 1.04	$ 3.18	$ 2.46
Diluted earnings per share (in dollars per share)	$ 1.49	$ 1.03	$ 3.15	$ 2.42