Goodwill and Identifiable Intangible Assets, Net - IdentifiableIntangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Identifiable Intangible Assets, Net
Gross Book Value	$ 139,884	$ 95,360
Accumulated Amortization	(63,840)	(52,925)
Amortization of identifiable intangible assets	17,404	8,185	$ 7,481
Future amortization expense of identifiable intangible assets
2018	13,786
2019	11,320
2020	9,252
2021	7,651
2022	6,041
Thereafter	27,994
Total	76,044
Customer relationships
Identifiable Intangible Assets, Net
Gross Book Value	98,244	57,230
Accumulated Amortization	$ (47,057)	(36,758)
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	$ 6,300	3,600
Accumulated Amortization	$ (5,478)	(3,433)
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
Noncompete agreements
Identifiable Intangible Assets, Net
Gross Book Value		2,890
Accumulated Amortization		(2,890)
Noncompete agreements | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Noncompete agreements | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	7 years
Trade names
Identifiable Intangible Assets, Net
Gross Book Value	$ 35,340	31,640
Accumulated Amortization	$ (11,305)	$ (9,844)
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 Non compete Agreements and Tradenames | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Customer Relationships Non compete Agreements and Tradenames | Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	25 years