Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Identifiable Intangible Assets, Net
Gross Book Value	$ 176,975	$ 139,884
Accumulated Amortization	(81,700)	(63,840)
Amortization of identifiable intangible assets	20,089	17,404	$ 8,185
Future amortization expense of identifiable intangible assets
2019	18,088
2020	15,103
2021	12,060
2022	9,866
2023	8,478
Thereafter	31,680
Total	95,275
Customer relationships
Identifiable Intangible Assets, Net
Gross Book Value	128,480	98,244
Accumulated Amortization	$ (60,731)	(47,057)
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	$ 9,100	6,300
Accumulated Amortization	$ (8,260)	(5,478)
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
Tradenames
Identifiable Intangible Assets, Net
Gross Book Value	$ 39,395	35,340
Accumulated Amortization	$ (12,709)	$ (11,305)
Tradenames | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Tradenames | 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