Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 848,620	$ 649,261
Accumulated Amortization	(437,886)	(372,081)
Finite-Lived Intangible Assets, Net	$ 410,734	277,180
Remaining Weighted Average Amortization Period	7 years 8 months 12 days
Indefinite-lived Intangible Assets [Line Items]
Intangible Assets	$ 851,620	652,261
Intangible Assets, Net	413,734	280,180
Engineering license
Indefinite-lived Intangible Assets [Line Items]
Intangible Assets	3,000	3,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	532,808	359,967
Accumulated Amortization	(213,915)	(165,715)
Finite-Lived Intangible Assets, Net	$ 318,893	194,252
Remaining Weighted Average Amortization Period	6 years 6 months
Backlog
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 144,704	135,578
Accumulated Amortization	(141,580)	(134,592)
Finite-Lived Intangible Assets, Net	$ 3,124	986
Remaining Weighted Average Amortization Period	2 years 9 months 18 days
Trade names
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 93,396	81,058
Accumulated Amortization	(26,145)	(21,559)
Finite-Lived Intangible Assets, Net	$ 67,251	59,499
Remaining Weighted Average Amortization Period	14 years 7 months 6 days
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 43,281	40,728
Accumulated Amortization	(32,868)	(30,168)
Finite-Lived Intangible Assets, Net	$ 10,413	10,560
Remaining Weighted Average Amortization Period	3 years 1 month 6 days
Patented rights and developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 22,719	22,482
Accumulated Amortization	(20,682)	(19,175)
Finite-Lived Intangible Assets, Net	$ 2,037	3,307
Remaining Weighted Average Amortization Period	2 years 2 months 12 days
Curriculum
Finite-Lived Intangible Assets [Line Items]
Intangible Assets	$ 11,712	9,448
Accumulated Amortization	(2,696)	(872)
Finite-Lived Intangible Assets, Net	$ 9,016	$ 8,576
Remaining Weighted Average Amortization Period	8 years 3 months 18 days