Acquisitions - Defined Benefit Plan (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Apr. 06, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Plan assets	$ 7,078		$ 2,225	$ 4,532
Unfunded projected benefit obligation	4,066		1,340
Plan liability	$ 11,144		$ 3,565	$ 6,444
Tec-Sem Group AG
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Plan assets		$ 5,100
Unfunded projected benefit obligation		2,800
Plan liability		$ 7,900
Defined benefit plan, type		us-gaap:PensionPlansDefinedBenefitMember
Defined benefit plan, sponsor location		us-gaap:ForeignPlanMember country:CH