CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Comprehensive Income (Loss):
Cumulative effect of change in accounting principle | ASU 2016-09	$ 0.2		$ 0.5	$ (0.3)
Balance (in shares) at Dec. 31, 2016		40,750,765			19,497,596
Balance at Dec. 31, 2016	279.7	$ 0.4	549.4	611.5	$ (879.5)	$ (2.1)
Comprehensive Income (Loss):
Net income	139.1			139.1
Change in fair value of cash flow swaps, net of reclassification adjustment	1.2					1.2
Comprehensive income	140.3			139.1		1.2
Share-based compensation	13.6		13.6
Issuance of common stock in connection with share-based payment arrangements (in shares)		219,222
Issuance of common stock in connection with share-based payment arrangements	0.0		0.0
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					74,670
Repurchase of common stock associated with net share settlements of employee share-based awards	(4.8)				$ (4.8)
Purchase of treasury shares (in shares)					584,696
Purchase of treasury shares	(34.8)				$ (34.8)
Balance (in shares) at Dec. 31, 2017		40,969,987			20,156,962
Balance at Dec. 31, 2017	394.2	$ 0.4	563.5	750.3	$ (919.1)	(0.9)
Comprehensive Income (Loss):
Cumulative effect of change in accounting principle | ASU 2014-09	9.2			9.2
Net income	168.0			168.0
Change in fair value of cash flow swaps, net of reclassification adjustment	1.5					1.5
Comprehensive income	169.5			168.0		1.5
Share-based compensation	10.5		10.5
Issuance of common stock in connection with share-based payment arrangements (in shares)		185,049
Issuance of common stock in connection with share-based payment arrangements	0.0
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					71,434
Repurchase of common stock associated with net share settlements of employee share-based awards	(4.8)				$ (4.8)
Purchase of treasury shares (in shares)					1,580,910
Purchase of treasury shares	(105.4)				$ (105.4)
Retirement of previously repurchased common stock (in shares)		(89,967)			(89,967)
Retirement of previously repurchased common stock	0.0		(1.1)	(4.8)	$ (5.9)
Balance (in shares) at Dec. 31, 2018		41,065,069			21,719,339
Balance at Dec. 31, 2018	473.2	$ 0.4	572.9	922.7	$ (1,023.4)	0.6
Comprehensive Income (Loss):
Cumulative effect of change in accounting principle | ASU 2014-09	0.0			0.2		(0.2)
Net income	184.4			184.4
Change in fair value of cash flow swaps, net of reclassification adjustment	(3.3)					(3.3)
Comprehensive income	181.1			184.4		(3.3)
Share-based compensation	12.5		12.5
Issuance of common stock in connection with share-based payment arrangements (in shares)		209,390
Issuance of common stock in connection with share-based payment arrangements	0.0
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					72,368
Repurchase of common stock associated with net share settlements of employee share-based awards	(5.2)				$ (5.2)
Purchase of treasury shares (in shares)					202,379
Purchase of treasury shares	(15.3)				$ (15.3)
Retirement of previously repurchased common stock (in shares)		(202,379)			(202,379)
Retirement of previously repurchased common stock	0.0		(2.5)	(12.8)	$ (15.3)
Balance (in shares) at Dec. 31, 2019		41,072,080			21,791,707
Balance at Dec. 31, 2019	$ 646.3	$ 0.4	$ 582.9	$ 1,094.5	$ (1,028.6)	$ (2.9)