Business Acquisitions - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands			3 Months Ended		6 Months Ended
	Jan. 03, 2020	Jun. 27, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Jan. 03, 2020	Sep. 30, 2020
Purchase price allocation
Goodwill			$ 788,027		$ 788,027			$ 784,882
Sales and results of operations
Sales			343,408	$ 321,482	662,202	$ 650,321
Operating income (loss)			(25,555)	(29,934)	(24,258)	(36,417)
Net income (loss) after taxes			(36,017)	(39,123)	(49,012)	(59,698)
Gain from changes in fair value of contingent consideration			1,260	(1,473)	684	(4,478)
PIXIA Corp
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred	$ 197,800						$ 245,200
Purchase price allocation
Accounts receivable, prepaids and other assets		$ 3,800
Deferred tax liability		(17,600)
Other net assets acquired (liabilities assumed)		(1,800)
Net identifiable assets acquired		72,200
Goodwill		173,000
Net assets acquired		$ 245,200
Weighted average useful life of intangible assets		4 years
Sales and results of operations
Sales			6,200	1,100	8,500	1,100
Operating income (loss)			(5,600)	(10,000)	(13,600)	(10,000)
Net income (loss) after taxes			(5,600)	(10,000)	(13,600)	(10,000)
Amortization			7,200	7,200	14,300	7,200
Acquisition-related expenses (income)			100	2,000	600	2,000
Estimated amortization expense related to the intangible assets
2021								28,700
2022								12,700
2023								7,300
2024								7,300
2025								7,300
Thereafter								3,200
PIXIA Corp | Trade names
Purchase price allocation
Indefinite intangible assets		$ 5,700
PIXIA Corp | Backlog
Purchase price allocation
Amortizable intangible assets		42,500
PIXIA Corp | Customer relationships
Purchase price allocation
Amortizable intangible assets		25,500
PIXIA Corp | Technology
Purchase price allocation
Amortizable intangible assets		$ 14,100
Delerrok Inc.
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred	45,100
Purchase price allocation
Accounts receivable	900						900
Deferred tax liability	(1,700)						(1,700)
Other net assets acquired (liabilities assumed)	(300)						(300)
Net identifiable assets acquired	14,700						14,700
Goodwill	30,400						30,400
Net assets acquired	$ 45,100						45,100
Weighted average useful life of intangible assets	10 years
Sales and results of operations
Sales			900	700	1,200	700
Operating income (loss)			(1,100)	(1,100)	(2,200)	(1,100)
Net income (loss) after taxes			(1,100)	(1,100)	(2,200)	(1,100)
Amortization			400	400	900	400
Acquisition-related expenses (income)			$ (200)	$ 700	200	$ 700
Gain from changes in fair value of contingent consideration					$ (900)
Estimated amortization expense related to the intangible assets
2021								1,700
2022								1,600
2023								1,600
2024								1,600
2025								1,600
Thereafter								$ 6,400
Delerrok Inc. | Trade names
Purchase price allocation
Indefinite intangible assets	$ 900						900
Delerrok Inc. | Technology
Purchase price allocation
Amortizable intangible assets	$ 14,900						$ 14,900