Acquisitions and Divestitures - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended
	Mar. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Jul. 31, 2018
Acquisitions
Compensation expense				$ 4,477	$ 2,720
Sales and results of operations
Sales				328,839	305,259
Operating income (loss)				(6,483)	(566)
Net loss after taxes				(20,575)	(6,587)
(Gain) loss for changes in fair values of contingent consideration				(3,005)	429
Purchase price allocation
Goodwill				582,549		$ 578,097
Nuvotronics
Sales and results of operations
Sales				2,800
Operating income (loss)				(400)
Net loss after taxes				(400)
Amortization				1,300
Acquisition-related expenses				500
(Gain) loss for changes in fair values of contingent consideration				$ (4,100)
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred	$ 66,800
Cash consideration paid	61,900
Contingent consideration	4,900
Period for contingent consideration contracts				12 months
Purchase price allocation
Accounts receivable and contract assets	2,600
Fixed assets	2,700
Accounts payable and accrued expenses	(1,800)
Deferred taxes	(3,200)
Other net assets acquired (liabilities assumed)	600
Net identifiable assets acquired	26,400
Goodwill	40,400
Net assets acquired	$ 66,800
Weighted average useful life of intangible assets	9 years
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 | Maximum
Estimated acquisition-date fair value of consideration
Contingent consideration	$ 8,000			$ 8,000
Nuvotronics | Trade names
Purchase price allocation
Indefinite intangible assets	1,500
Nuvotronics | Technology
Purchase price allocation
Amortizable intangible assets	22,700
Nuvotronics | Customer relationships
Purchase price allocation
Amortizable intangible assets	600
Nuvotronics | Backlog
Purchase price allocation
Amortizable intangible assets	1,400
Nuvotronics | Non-compete agreements
Purchase price allocation
Amortizable intangible assets	$ 500
GRIDSMART
Sales and results of operations
Sales				4,100
Operating income (loss)				(1,700)
Net loss after taxes				(1,700)
Amortization				1,300
Acquisition-related expenses				500
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 taxes		(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
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 | Technology
Purchase price allocation
Amortizable intangible assets		25,700
GRIDSMART | Customer relationships
Purchase price allocation
Amortizable intangible assets		$ 3,600
Trafficware
Sales and results of operations
Sales				9,100	10,500
Operating income (loss)				(3,000)	(3,300)
Net loss after taxes				(3,000)	(3,300)
Amortization				2,800	4,300
Acquisition-related expenses				500	$ 1,400
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
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 | Technology
Purchase price allocation
Amortizable intangible assets			43,300
Trafficware | Customer relationships
Purchase price allocation
Amortizable intangible assets			21,900
Trafficware | Backlog
Purchase price allocation
Amortizable intangible assets			$ 4,800
Shield Aviation | Maximum
Estimated acquisition-date fair value of consideration
Contingent consideration				$ 10,000			$ 10,000