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 at Dec. 31, 2017	$ 912.3	$ 0.1	$ 618.3	$ (39.5)	$ (3.7)	$ 337.1
Balance (in shares) at Dec. 31, 2017		50,600,000		1,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		400,000
Employee equity plans activity	6.1		6.1
Treasury stock	(0.1)			$ (0.1)
Other comprehensive income	0.4				0.4
Net loss	(4.9)					(4.9)
Balance at Mar. 31, 2018	881.3	$ 0.1	624.4	$ (39.6)	(3.3)	299.7
Balance (in shares) at Mar. 31, 2018		51,000,000		1,200,000
Balance at Dec. 31, 2018	$ 1,010.9	$ 0.1	688.6	$ (39.6)	(5.5)	367.3
Balance (in shares) at Dec. 31, 2018	52,400,000	52,400,000		1,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity (in shares)		200,000
Employee equity plans activity	$ 1.6		1.6
Other comprehensive income	1.0				1.0
Net loss	(26.0)					(26.0)
Balance at Mar. 31, 2019	$ 987.5	$ 0.1	$ 690.2	$ (39.6)	$ (4.5)	$ 341.3
Balance (in shares) at Mar. 31, 2019	52,600,000	52,600,000		1,200,000