Acquisitions and Divestitures - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands		1 Months Ended			3 Months Ended		6 Months Ended			15 Months Ended
	Jan. 03, 2020	Mar. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Jan. 03, 2020	Mar. 31, 2019	Jan. 03, 2020	Sep. 30, 2019
Purchase price allocation
Goodwill					$ 781,683		$ 781,683				$ 578,097
Sales and results of operations
Sales					321,482	$ 337,339	650,321		$ 642,598
Operating income (loss)					(29,934)	(6,541)	(36,417)		(7,107)
Net income (loss) after taxes					(39,123)	(9,392)	(59,698)		(15,979)
(Gain) loss for changes in fair values of contingent consideration					(1,473)	241	(4,478)		670
PIXIA Corp
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred	$ 243,800
Cash consideration paid	197,600							$ 247,600
Purchase price allocation
Accounts receivable, prepaids and other assets	3,900							3,900		$ 3,900
Deferred tax liability	(18,300)							(18,300)		(18,300)
Other net assets acquired (liabilities assumed)	(1,800)							(1,800)		(1,800)
Net identifiable assets acquired	71,600							71,600		71,600
Goodwill	172,100							172,100		172,100
Net assets acquired	$ 243,700							243,700		243,700
Weighted average useful life of intangible assets	4 years
Sales and results of operations
Sales					1,100		1,100
Operating income (loss)					(10,000)		(10,000)
Net income (loss) after taxes					(10,000)		(10,000)
Amortization					7,200		7,200
Acquisition-related expenses					2,000		2,000
Estimated amortization expense related to the intangible assets
2020											21,500
2021											28,700
2022											12,700
2023											7,300
2024											7,300
Thereafter											10,500
PIXIA Corp | Trade names
Purchase price allocation
Indefinite intangible assets	$ 5,700							5,700		5,700
PIXIA Corp | Backlog
Purchase price allocation
Amortizable intangible assets	42,500							42,500		42,500
PIXIA Corp | Customer relationships
Purchase price allocation
Amortizable intangible assets	25,500							25,500		25,500
PIXIA Corp | Technology
Purchase price allocation
Amortizable intangible assets	14,100							14,100		14,100
Nuvotronics
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred		$ 66,800
Cash consideration paid		61,900
Contingent consideration for certain goals		8,000					$ 8,000
Contingent consideration		4,900				4,900			4,900
Period for contingent consideration contracts							12 months
Purchase price allocation
Accounts receivable and contract assets		2,600				2,600			2,600
Fixed assets		2,700				2,700			2,700
Accounts payable and accrued expenses		(1,800)				(1,800)			(1,800)
Deferred tax liability		(3,200)				(3,200)			(3,200)
Other net assets acquired (liabilities assumed)		(600)				(600)			(600)
Net identifiable assets acquired		26,400				26,400			26,400
Goodwill		40,400				40,400			40,400
Net assets acquired		$ 66,800				66,800			66,800
Weighted average useful life of intangible assets		9 years
Sales and results of operations
Sales					3,200	700	$ 6,000		700
Operating income (loss)					(4,500)	(1,700)	(4,900)		(1,700)
Net income (loss) after taxes					(4,500)	(1,700)	(4,900)		(1,700)
Amortization					900	100	2,200		100
Acquisition-related expenses					700	1,800	1,300		1,800
(Gain) loss for changes in fair values of contingent consideration							(4,200)
Estimated amortization expense related to the intangible assets
2020											4,000
2021											3,000
2022											3,000
2023											2,900
2024											2,700
Thereafter											10,100
Nuvotronics | Trade names
Purchase price allocation
Indefinite intangible assets		$ 1,500				1,500			1,500
Nuvotronics | Backlog
Purchase price allocation
Amortizable intangible assets		1,400				1,400			1,400
Nuvotronics | Customer relationships
Purchase price allocation
Amortizable intangible assets		600				600			600
Nuvotronics | Technology
Purchase price allocation
Amortizable intangible assets		22,700				22,700			22,700
Nuvotronics | Non-compete agreements
Purchase price allocation
Amortizable intangible assets		$ 500				500			500
Delerrok Inc.
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred	45,100
Cash consideration paid	37,000									43,500
Contingent consideration for certain goals							2,000
Contingent consideration	1,600							1,600		1,600
Purchase price allocation
Accounts receivable	900							900		900
Deferred tax liability	(2,000)							(2,000)		(2,000)
Other net assets acquired (liabilities assumed)	(200)							(200)		(200)
Net identifiable assets acquired	14,500							14,500		14,500
Goodwill	30,600							30,600		30,600
Net assets acquired	$ 45,100							45,100		45,100
Weighted average useful life of intangible assets	8 years
Sales and results of operations
Sales					700		700
Operating income (loss)					(1,100)		(1,100)
Net income (loss) after taxes					(1,100)		(1,100)
Amortization					400		400
Acquisition-related expenses					700		700
Estimated amortization expense related to the intangible assets
2020											1,300
2021											1,700
2022											1,600
2023											1,600
2024											1,600
Thereafter											8,000
Delerrok Inc. | Trade names
Purchase price allocation
Indefinite intangible assets	$ 900							900		900
Delerrok Inc. | Technology
Purchase price allocation
Amortizable intangible assets	$ 14,900							$ 14,900		$ 14,900
GRIDSMART
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred			$ 86,800
Purchase price allocation
Accounts receivable			1,700
Inventory			4,300
Accounts payable and accrued expenses			(1,900)
Deferred tax liability			(3,300)
Other net assets acquired (liabilities assumed)			(500)
Net identifiable assets acquired			33,000
Goodwill			53,800
Net assets acquired			$ 86,800
Weighted average useful life of intangible assets			8 years
Sales and results of operations
Sales					7,700	6,300	11,900		6,300
Operating income (loss)					900	(2,000)	(800)		(2,000)
Net income (loss) after taxes					900	(2,000)	(800)		(2,000)
Amortization					1,300	1,400	2,700		1,400
Acquisition-related expenses					(100)	1,800	400		1,800
Estimated amortization expense related to the intangible assets
2020											5,300
2021											3,900
2022											3,500
2023											3,500
2024											3,500
Thereafter											8,100
GRIDSMART | Trade names
Purchase price allocation
Indefinite intangible assets			$ 2,400
GRIDSMART | Customer relationships
Purchase price allocation
Amortizable intangible assets			3,600
GRIDSMART | Technology
Purchase price allocation
Amortizable intangible assets			$ 25,700
Trafficware
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred				$ 237,200
Purchase price allocation
Accounts receivable				10,400
Inventory				9,900
Accounts payable and accrued expenses				(9,500)
Other net assets acquired (liabilities assumed)				(2,000)
Net identifiable assets acquired				83,400
Goodwill				153,800
Net assets acquired				$ 237,200
Weighted average useful life of intangible assets				7 years
Sales and results of operations
Sales					14,000	11,700	23,000		22,200
Operating income (loss)					(200)	(5,200)	(3,200)		(8,500)
Net income (loss) after taxes					(200)	(5,200)	(3,200)		(8,500)
Amortization					2,800	5,300	5,700		9,600
Acquisition-related expenses					$ 400	$ 2,100	900		$ 3,500
Estimated amortization expense related to the intangible assets
2020											11,400
2021											11,400
2022											11,400
2023											6,400
2024											5,900
Thereafter											$ 12,900
Trafficware | Trade names
Purchase price allocation
Indefinite intangible assets				$ 4,600
Trafficware | Backlog
Purchase price allocation
Amortizable intangible assets				4,800
Trafficware | Customer relationships
Purchase price allocation
Amortizable intangible assets				21,900
Trafficware | Technology
Purchase price allocation
Amortizable intangible assets				$ 43,300
Shield Aviation
Estimated acquisition-date fair value of consideration
Contingent consideration for certain goals							$ 10,000