Acquisitions and Divestitures - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended			4 Months Ended	6 Months Ended
	Feb. 21, 2018	Nov. 30, 2016	Jul. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Feb. 21, 2018	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Sales and results of operations
Sales				$ 278,586	$ 248,040			$ 526,977	$ 492,410
Operating loss				(1,679)	(6,084)			(13,581)	(11,707)
Net loss after taxes				(2,011)	461			(11,797)	(2,407)
Estimated acquisition-date fair value of consideration
Compensation expense				870	1,015			2,497	3,191
Purchase price allocation
Goodwill				330,538				330,538		$ 321,562
MotionDSP
Sales and results of operations
Sales				100				100
Operating loss				(200)				(200)
Net loss after taxes				(200)				(200)
Amortization				100				100
Acquisition-related expenses				400				600
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred							$ 9,500
Cash consideration paid	$ 5,000						9,700
Purchase price allocation
Accounts payable and accrued expenses	(300)						(300)
Other noncurrent liabilities	(800)						(800)
Other net assets acquired (liabilities assumed)	(900)						(900)
Net identifiable assets acquired	2,800						2,800
Goodwill	6,700						6,700
Net assets acquired	$ 9,500						9,500
Weighted average useful life of intangible assets	7 years
Estimated amortization expense related to the intangible assets
2018										400
2019										700
2020										700
2021										700
2022										700
Thereafter										1,600
MotionDSP | Trade names
Purchase price allocation
Indefinite intangible assets	$ 100						100
MotionDSP | Customer relationships
Purchase price allocation
Amortizable intangible assets	200						200
MotionDSP | Technology
Purchase price allocation
Amortizable intangible assets	$ 4,500						$ 4,500
Deltenna
Sales and results of operations
Sales				100				100
Operating loss				(100)				(200)
Net loss after taxes				(100)				(200)
Amortization								100
Acquisition-related expenses				(200)				(200)
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred			$ 5,300
Cash consideration paid			4,000
Contingent consideration			1,300
Purchase price allocation
Other net assets acquired (liabilities assumed)			(300)
Net identifiable assets acquired			1,800
Goodwill			3,500
Net assets acquired			$ 5,300
Weighted average useful life of intangible assets			8 years
Estimated amortization expense related to the intangible assets
2018										300
2019										300
2020										300
2021										300
2022										300
Thereafter										800
Deltenna | Maximum
Estimated acquisition-date fair value of consideration
Contingent consideration			$ 7,600	7,600				7,600
Deltenna | Customer relationships
Purchase price allocation
Amortizable intangible assets			1,000
Deltenna | Technology
Purchase price allocation
Amortizable intangible assets			$ 1,100
Vocality
Sales and results of operations
Sales				700	700			2,900	800
Operating loss				(900)	(500)			(800)	(1,600)
Net loss after taxes				(800)	(600)			(700)	(1,500)
Amortization				$ 200	200			400	200
Acquisition-related expenses					$ 400			$ 600	$ 1,200
Estimated acquisition-date fair value of consideration
Compensation expense						$ 400
Fair value of consideration transferred		$ 9,600
Cash consideration paid		9,700
Contingent consideration		300
Cash paid related to compensation expenses		400
Purchase price allocation
Inventory		1,700
Accounts payable and accrued expenses		(400)
Other net assets acquired (liabilities assumed)		(500)
Net identifiable assets acquired		5,700
Goodwill		3,900
Net assets acquired		$ 9,600
Weighted average useful life of intangible assets		9 years
Estimated amortization expense related to the intangible assets
2018										800
2019										800
2020										700
2021										600
2022										500
Thereafter										$ 1,300
Vocality | Trade names
Purchase price allocation
Indefinite intangible assets		$ 400
Vocality | Customer relationships
Purchase price allocation
Amortizable intangible assets		2,100
Vocality | Technology
Purchase price allocation
Amortizable intangible assets		$ 2,400