Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Identifiable Intangible Assets, Net
Gross Book Value	$ 268,658		$ 268,658		$ 176,975
Accumulated Amortization	(101,922)		(101,922)		(81,700)
Amortization of identifiable intangible assets	7,200	$ 5,300	20,221	$ 14,102
Future amortization expense of identifiable intangible assets
2019 (remainder of the year)	6,844		6,844
2020	23,213		23,213
2021	19,158		19,158
2022	16,536		16,536
2023	15,082		15,082
Thereafter	85,903		85,903
Total	166,736		166,736
Customer Relationships
Identifiable Intangible Assets, Net
Gross Book Value	182,963		182,963		128,480
Accumulated Amortization	(75,455)		$ (75,455)		(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	13,700		$ 13,700		9,100
Accumulated Amortization	(11,906)		$ (11,906)		(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		$ 71,995		39,395
Accumulated Amortization	$ (14,561)		$ (14,561)		$ (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