Stock Plans - RSAs, RSUs, PSAs and PSUs (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
RSAs, RSUs, PSAs and PSUs
Number of Shares
Outstanding at the beginning of the period (in shares)	1,880	1,949	1,398
Granted (in shares)	1,257	674	1,166
Performance award adjustments (in shares)	(5)	(25)
Assumed from Ultratech (in shares)		338
Vested (in shares)	(523)	(831)	(349)
Forfeited (in shares)	(391)	(225)	(266)
Outstanding at the end of the period (in shares)	2,218	1,880	1,949
Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 25.41	$ 23.85	$ 31.97
Granted (in dollars per share)	17.37	29.22	17.59
Performance award adjustments (in dollars per share)	32.67	20.95
Assumed from Ultratech (in dollars per share)		31.75
Vested (in dollars per share)	26.39	27.67	32.73
Forfeited (in dollars per share)	24.66	26.29	27.31
Outstanding at the end of the period (in dollars per share)	$ 20.74	$ 25.41	$ 23.85
Total fair value of shares vested	$ 9.1	$ 22.3	$ 7.5
PSAs and PSUs | Minimum
Weighted Average Grant Date Fair Value
Vesting period	1 year
PSAs and PSUs | Maximum
Weighted Average Grant Date Fair Value
Vesting period	5 years