Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	$0.001 Par Value Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Retained Earnings
Balance (in shares) at Dec. 31, 2017		(50,600,000)		(1,200,000)
Balance at Dec. 31, 2017	$ 912.3	$ 0.1	$ 618.4	$ (39.5)	$ (3.8)	$ 337.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		600,000
Employee equity plans activity	14.0		14.1	$ (0.1)
Net loss	45.2					45.2
Other comprehensive income	(0.7)				(0.7)
Balance (in shares) at Jun. 30, 2018		(51,200,000)		(1,200,000)
Balance at Jun. 30, 2018	938.3	$ 0.1	632.5	$ (39.6)	(4.5)	349.8
Balance (in shares) at Mar. 31, 2018		(51,000,000.0)		(1,200,000)
Balance at Mar. 31, 2018	881.3	$ 0.1	624.4	$ (39.6)	(3.3)	299.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		200,000
Employee equity plans activity	8.1		8.1
Net loss	50.1					50.1
Other comprehensive income	(1.2)				(1.2)
Balance (in shares) at Jun. 30, 2018		(51,200,000)		(1,200,000)
Balance at Jun. 30, 2018	$ 938.3	$ 0.1	632.5	$ (39.6)	(4.5)	349.8
Balance (in shares) at Dec. 31, 2018	(52,400,000)	(52,400,000)		(1,200,000)
Balance at Dec. 31, 2018	$ 1,010.9	$ 0.1	688.6	$ (39.6)	(5.5)	367.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		300,000
Employee equity plans activity	13.1		13.2	$ (0.1)
Net loss	(35.6)					(35.6)
Other comprehensive income	$ 0.5				0.5
Balance (in shares) at Jun. 30, 2019	(52,700,000)	(52,700,000)		(1,200,000)
Balance at Jun. 30, 2019	$ 988.9	$ 0.1	701.8	$ (39.7)	(5.0)	331.7
Balance (in shares) at Mar. 31, 2019		(52,600,000)		(1,200,000)
Balance at Mar. 31, 2019	987.3	$ 0.1	690.1	$ (39.6)	(4.5)	341.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		100,000
Employee equity plans activity	11.6		11.7	$ (0.1)
Net loss	(9.5)					(9.5)
Other comprehensive income	$ (0.5)				(0.5)
Balance (in shares) at Jun. 30, 2019	(52,700,000)	(52,700,000)		(1,200,000)
Balance at Jun. 30, 2019	$ 988.9	$ 0.1	$ 701.8	$ (39.7)	$ (5.0)	$ 331.7