Acquisitions and Divestitures - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended			9 Months Ended
	Feb. 21, 2018	Nov. 30, 2016	Jul. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017
Sales and results of operations
Sales				$ 296,212	$ 266,184		$ 823,189	$ 758,594
Operating income (loss)				10,290	(6,848)		(3,291)	(18,579)
Net income (loss) after taxes				6,291	(21,957)		(5,506)	(24,364)
Estimated acquisition-date fair value of consideration
Compensation expense				2,603	395		5,100	3,586
Purchase price allocation
Goodwill				327,964			327,964		$ 321,562
MotionDSP
Sales and results of operations
Sales				300			400
Operating income (loss)				(200)			(1,000)
Net income (loss) after taxes				(200)			(1,000)
Amortization				200			200
Acquisition-related expenses				100			700
Estimated acquisition-date fair value of consideration
Cash consideration paid	$ 4,800
Purchase price allocation
Accounts payable and accrued expenses	(300)
Other noncurrent liabilities	(800)
Other net assets acquired (liabilities assumed)	(900)
Net identifiable assets acquired	2,800
Goodwill	6,700
Net assets acquired	$ 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
MotionDSP | Customer relationships
Purchase price allocation
Amortizable intangible assets	200
MotionDSP | Technology
Purchase price allocation
Amortizable intangible assets	$ 4,500
Deltenna
Sales and results of operations
Sales				300			300
Operating income (loss)				100			100
Net income (loss) after taxes				100			100
Amortization				100			200
Acquisition-related expenses				(100)			(300)
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									700
Deltenna | Maximum
Estimated acquisition-date fair value of consideration
Contingent consideration			$ 7,600	7,100			7,100
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				1,700	400		4,600	1,200
Operating income (loss)				300	(700)		(1,000)	(2,300)
Net income (loss) after taxes				300	(600)		(1,000)	(2,100)
Amortization				$ 200	200		600	400
Acquisition-related expenses					$ 300		$ 600	$ 1,500
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									700
2020									600
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