Acquisitions and Divestitures - Consolidated Business Acquisitions (Details) - USD ($) $ in Thousands		1 Months Ended			3 Months Ended
	Feb. 21, 2018	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Oct. 01, 2018	Sep. 30, 2018
Sales and results of operations
Sales					$ 305,259	$ 248,391
Operating income (loss)					(566)	(11,902)
Net loss after taxes					(6,587)	(9,786)
Estimated acquisition-date fair value of consideration
Compensation expense					2,720	$ 1,627
Purchase price allocation
Goodwill					484,329		$ 333,626	$ 333,626
Trafficware
Sales and results of operations
Sales					10,500
Operating income (loss)					(3,300)
Net loss after taxes					(3,300)
Amortization					4,300
Acquisition-related (benefit) expenses					1,400
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred			$ 237,600
Cash consideration paid			239,200
Receivable due from the sellers			1,600
Purchase price allocation
Amortizable intangible assets			4,800
Accounts receivable			10,400
Inventory			9,400
Accounts payable and accrued expenses			(6,500)
Other net assets acquired (liabilities assumed)			(2,000)
Net identifiable assets acquired			85,900
Goodwill			151,700
Net assets acquired			$ 237,600
Weighted average useful life of intangible assets			7 years
Estimated amortization expense related to the intangible assets
2019								15,300
2020								11,400
2021								11,400
2022								11,400
2023								6,400
Thereafter								18,800
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
Shield Aviation
Sales and results of operations
Operating income (loss)					(900)
Net loss after taxes					(900)
Amortization					200
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred				$ 12,800
Extinguishment of debt				5,200
Cash consideration paid				1,300
Hold back consideration				700
Contingent consideration				5,600
Purchase price allocation
Other net assets acquired				300
Net identifiable assets acquired				6,300
Goodwill				6,500
Net assets acquired				12,800
Estimated amortization expense related to the intangible assets
2019					800
2020					800
2021					800
2022					800
2023					800
Thereafter					2,100
Shield Aviation | Maximum
Estimated acquisition-date fair value of consideration
Contingent consideration				10,000	10,000
Shield Aviation | Technology
Purchase price allocation
Amortizable intangible assets				$ 6,000
MotionDSP
Sales and results of operations
Sales					200
Operating income (loss)					(400)
Net loss after taxes					(400)
Amortization					200
Acquisition-related (benefit) expenses					$ 100
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
2019								700
2020								700
2021								700
2022								700
2023								700
Thereafter								$ 800
MotionDSP | Trade names
Purchase price allocation
Indefinite intangible assets	$ 100
MotionDSP | Technology
Purchase price allocation
Amortizable intangible assets	4,500
MotionDSP | Customer relationships
Purchase price allocation
Amortizable intangible assets	$ 200
GRIDSMART | Subsequent event
Estimated acquisition-date fair value of consideration
Fair value of consideration transferred		$ 87,000