Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Identifiable Intangible Assets, Net
Gross Book Value	$ 262,456	$ 176,975
Accumulated Amortization	(102,482)	(81,700)
Amortization of identifiable intangible assets	27,082	20,089	$ 17,404
Future amortization expense of identifiable intangible assets
2020	23,246
2021	19,191
2022	16,545
2023	15,082
2024	13,732
Thereafter	72,178
Total	159,974
Customer Relationships
Identifiable Intangible Assets, Net
Gross Book Value	183,061	128,480
Accumulated Amortization	$ (80,813)	(60,731)
Customer Relationships | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Customer Relationships | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	15 years
Backlog
Identifiable Intangible Assets, Net
Gross Book Value	$ 7,400	9,100
Accumulated Amortization	$ (6,388)	(8,260)
Backlog | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Backlog | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Trade Names
Identifiable Intangible Assets, Net
Gross Book Value	$ 71,995	39,395
Accumulated Amortization	$ (15,281)	$ (12,709)
Trade Names | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Trade Names | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	25 years
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