CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Treasury Stock, At Cost	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balances (in shares) at Dec. 31, 2017		37,094,000
Balances at Dec. 31, 2017	$ 211.8	$ 0.4	$ 186.5	$ (21.8)	$ 44.8	$ 1.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	2.8		2.8
Issuance of restricted stock (in shares)		117,000
Issuance of restricted stock	0.0		(1.7)	1.7
Stock withheld for employee taxes (in shares)		(62,000)
Stock withheld for employee taxes	(1.9)			(1.9)
Proceeds from issuance of common stock (in shares)		419,000
Proceeds from issuance of common stock	5.4		(0.6)	6.0
Dividends	$ (297.1)				(297.1)
Purchase of treasury shares (in shares)	(232,550)	(233,000)
Purchase of treasury shares	$ (9.1)			(9.1)
Discontinued France operations entities cumulative translation adjustment	4.1					4.1
Change in cumulative translation adjustment	(3.0)					(3.0)
Net income	224.7				224.7
Balances (in shares) at Dec. 31, 2018		37,335,000
Balances at Dec. 31, 2018	137.7	$ 0.4	187.0	(25.1)	(27.6)	3.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	5.4		5.4
Issuance of restricted stock (in shares)		109,000
Issuance of restricted stock	0.0		(1.8)	1.8
Stock withheld for employee taxes (in shares)		(39,000)
Stock withheld for employee taxes	(0.9)			(0.9)
Proceeds from issuance of common stock (in shares)		230,000
Proceeds from issuance of common stock	2.1		(1.7)	3.8
Dividends	(18.1)				(18.1)
Issuance of shares under employee stock purchase plan (shares)		44,000
Issuance of shares under employee stock purchase plan	0.8		0.8
Change in cumulative translation adjustment	0.0
Net income	48.5				48.5
Balances (in shares) at Dec. 31, 2019		37,679,000
Balances at Dec. 31, 2019	175.5	$ 0.4	189.7	(20.4)	2.8	3.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	4.7		4.7
Issuance of restricted stock (in shares)		42,000
Issuance of restricted stock	0.0		(0.7)	0.7
Stock withheld for employee taxes (in shares)		(47,000)
Stock withheld for employee taxes	(1.4)			(1.4)
Proceeds from issuance of common stock (in shares)		221,000
Proceeds from issuance of common stock	3.3		(1.0)	4.3
Dividends	$ (134.7)				(134.7)
Purchase of treasury shares (in shares)	(392,337)	(392,000)
Purchase of treasury shares	$ (7.2)			(7.2)
Issuance of shares under employee stock purchase plan (shares)		49,000
Issuance of shares under employee stock purchase plan	0.8		0.8
Change in cumulative translation adjustment	0.4					0.4
Net income	65.4				65.4
Balances (in shares) at Dec. 31, 2020		37,552,000
Balances at Dec. 31, 2020	$ 106.8	$ 0.4	$ 193.5	$ (24.0)	$ (66.5)	$ 3.4