Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock Issued	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Dec. 31, 2018	$ 567.0	$ 0.5	$ 283.3	$ (90.6)	$ 381.6	$ (7.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, net of shares withheld for employee taxes			(2.2)
Stock-based compensation expense			7.2
Repurchase of common stock				(8.1)
Net income	41.5				41.5
Dividends declared					(15.3)
Other comprehensive gains (losses)						1.5
Ending balance at Sep. 30, 2019	$ 591.6	$ 0.5	288.3	$ (98.7)	407.8	(6.3)
Beginning balance (in shares) at Dec. 31, 2018		52.5		6.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock based instruments, net of shares withheld for employee taxes (in shares)		0.2
Repurchase of common stock (in shares)				(0.3)
Ending balance (in shares) at Sep. 30, 2019	45.6	52.7		7.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.33
Beginning balance at Jun. 30, 2019	$ 580.8	$ 0.5	285.3	$ (90.6)	390.4	(4.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, net of shares withheld for employee taxes			(0.1)
Stock-based compensation expense			3.1
Repurchase of common stock				(8.1)
Net income	22.5				22.5
Dividends declared					(5.1)
Other comprehensive gains (losses)						(1.5)
Ending balance at Sep. 30, 2019	$ 591.6	$ 0.5	288.3	$ (98.7)	407.8	(6.3)
Beginning balance (in shares) at Jun. 30, 2019		52.7		6.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock based instruments, net of shares withheld for employee taxes (in shares)		0.0
Repurchase of common stock (in shares)				(0.3)
Ending balance (in shares) at Sep. 30, 2019	45.6	52.7		7.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.11
Beginning balance at Dec. 31, 2019	$ 591.9	$ 0.5	290.6	$ (112.6)	418.5	(5.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, net of shares withheld for employee taxes			(2.5)
Stock-based compensation expense			6.7
Repurchase of common stock				(5.4)
Net income	44.2				44.2
Dividends declared					(16.1)
Other comprehensive gains (losses)						(0.2)
Ending balance at Sep. 30, 2020	$ 618.6	$ 0.5	294.8	$ (118.0)	446.6	(5.3)
Beginning balance (in shares) at Dec. 31, 2019		52.7		7.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock based instruments, net of shares withheld for employee taxes (in shares)		0.2
Repurchase of common stock (in shares)				(0.2)
Ending balance (in shares) at Sep. 30, 2020	45.1	52.9		7.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 360,000
Beginning balance at Jun. 30, 2020	$ 597.0	$ 0.5	292.3	$ (118.0)	428.7	(6.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued, net of shares withheld for employee taxes			(0.1)
Stock-based compensation expense			2.6
Repurchase of common stock				0.0
Net income	23.0				23.0
Dividends declared					(5.1)
Other comprehensive gains (losses)						1.2
Ending balance at Sep. 30, 2020	$ 618.6	$ 0.5	$ 294.8	$ (118.0)	$ 446.6	$ (5.3)
Beginning balance (in shares) at Jun. 30, 2020		52.9		7.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock based instruments, net of shares withheld for employee taxes (in shares)		0.0
Repurchase of common stock (in shares)				0.0
Ending balance (in shares) at Sep. 30, 2020	45.1	52.9		7.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 120,000