Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	11 years 8 months 12 days
Gross Book Value	$ 366,987	$ 262,456
Accumulated Amortization	(135,180)	(102,482)
Amortization of identifiable intangible assets	32,698	27,082	$ 20,089
Future amortization expense of identifiable intangible assets
2021	32,344
2022	27,412
2023	23,514
2024	22,164
2025	19,977
Thereafter	106,396
Total	$ 231,807
Customer Relationships
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	8 years
Gross Book Value	$ 255,692	183,061
Accumulated Amortization	$ (103,919)	(80,813)
Customer Relationships | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	8 years
Backlog
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Gross Book Value	$ 19,800	7,400
Accumulated Amortization	$ (12,600)	(6,388)
Backlog | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Trade Name
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	20 years 6 months
Gross Book Value	$ 91,495	71,995
Accumulated Amortization	$ (18,661)	$ (15,281)
Trade Name | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	20 years 6 months
Customer Relationships Noncompete Agreements and Tradenames | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Customer Relationships Noncompete Agreements and Tradenames | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	25 years