Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]
Beginning Balance at Dec. 31, 2018	$ 1,873.2	$ 0.1	$ 793.9	$ 1,084.8	$ (5.6)
Beginning Balance, Shares at Dec. 31, 2018		54,039,554
Net issuance under stock-based plans	22.5		22.5
Net issuance under stock-based plans, Shares		192,218
Stock-based compensation	27.8		27.8
Cash dividend	(10.8)			(10.8)
Comprehensive income (net of tax):
Net income	12.5			12.5
Other comprehensive income (loss)	(4.3)				(4.3)
Ending Balance at Mar. 31, 2019	1,920.9	$ 0.1	844.2	1,086.5	(9.9)
Ending Balance, Shares at Mar. 31, 2019		54,231,772
Beginning Balance at Dec. 31, 2018	1,873.2	$ 0.1	793.9	1,084.8	(5.6)
Beginning Balance, Shares at Dec. 31, 2018		54,039,554
Comprehensive income (net of tax):
Net income	97.6
Ending Balance at Sep. 30, 2019	1,973.5	$ 0.1	856.4	1,149.5	(32.5)
Ending Balance, Shares at Sep. 30, 2019		54,496,664
Beginning Balance at Mar. 31, 2019	1,920.9	$ 0.1	844.2	1,086.5	(9.9)
Beginning Balance, Shares at Mar. 31, 2019		54,231,772
Net issuance under stock-based plans	(2.1)		(2.1)
Net issuance under stock-based plans, Shares		247,920
Stock-based compensation	7.2		7.2
Cash dividend	(10.9)			(10.9)
Stock dividends accrued			0.2	(0.2)
Comprehensive income (net of tax):
Net income	37.7			37.7
Other comprehensive income (loss)	(7.3)				(7.3)
Ending Balance at Jun. 30, 2019	1,945.5	$ 0.1	849.5	1,113.1	(17.2)
Ending Balance, Shares at Jun. 30, 2019		54,479,692
Net issuance under stock-based plans	(0.6)		(0.6)
Net issuance under stock-based plans, Shares		16,972
Stock-based compensation	7.4		7.4
Cash dividend	(10.9)			(10.9)
Stock dividends accrued			0.1	(0.1)
Comprehensive income (net of tax):
Net income	47.4			47.4
Other comprehensive income (loss)	(15.3)				(15.3)
Ending Balance at Sep. 30, 2019	1,973.5	$ 0.1	856.4	1,149.5	(32.5)
Ending Balance, Shares at Sep. 30, 2019		54,496,664
Beginning Balance at Dec. 31, 2019	2,023.3	$ 0.1	864.3	1,181.2	(22.3)
Beginning Balance, Shares at Dec. 31, 2019		54,596,183
Net issuance under stock-based plans	(20.4)		(20.4)
Net issuance under stock-based plans, Shares		276,800
Stock-based compensation	8.5		8.5
Cash dividend	(11.0)			(11.0)
Comprehensive income (net of tax):
Net income	69.1			69.1
Other comprehensive income (loss)	(17.0)				(17.0)
Ending Balance at Mar. 31, 2020	2,052.5	$ 0.1	852.4	1,239.3	(39.3)
Ending Balance, Shares at Mar. 31, 2020		54,872,983
Beginning Balance at Dec. 31, 2019	2,023.3	$ 0.1	864.3	1,181.2	(22.3)
Beginning Balance, Shares at Dec. 31, 2019		54,596,183
Comprehensive income (net of tax):
Net income	234.5
Ending Balance at Sep. 30, 2020	2,226.8	$ 0.1	861.6	1,382.7	(17.6)
Ending Balance, Shares at Sep. 30, 2020		55,135,910
Beginning Balance at Mar. 31, 2020	2,052.5	$ 0.1	852.4	1,239.3	(39.3)
Beginning Balance, Shares at Mar. 31, 2020		54,872,983
Net issuance under stock-based plans	(0.5)		(0.5)
Net issuance under stock-based plans, Shares		205,850
Stock-based compensation	6.8		6.8
Cash dividend	(11.0)			(11.0)
Comprehensive income (net of tax):
Net income	73.7			73.7
Other comprehensive income (loss)	5.1				5.1
Ending Balance at Jun. 30, 2020	2,126.6	$ 0.1	858.7	1,302.0	(34.2)
Ending Balance, Shares at Jun. 30, 2020		55,078,833
Net issuance under stock-based plans	(4.5)		(4.5)
Net issuance under stock-based plans, Shares		57,077
Stock-based compensation	7.4		7.4
Cash dividend	(11.0)			(11.0)
Comprehensive income (net of tax):
Net income	91.7			91.7
Other comprehensive income (loss)	16.6				16.6
Ending Balance at Sep. 30, 2020	$ 2,226.8	$ 0.1	$ 861.6	$ 1,382.7	$ (17.6)
Ending Balance, Shares at Sep. 30, 2020		55,135,910