Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 83,830	$ 19,979
Finite-Lived Intangible Assets, Accumulated Amortization	(32,276)	(10,915)
Finite-Lived Intangible Assets, Net	51,554	9,064
Value of Business Acquired
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	42,788	8,975
Finite-Lived Intangible Assets, Accumulated Amortization	(25,882)	(7,867)
Finite-Lived Intangible Assets, Net	16,906	1,108
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	34,661	10,284
Finite-Lived Intangible Assets, Accumulated Amortization	(5,546)	(2,784)
Finite-Lived Intangible Assets, Net	$ 29,115	$ 7,500
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	8 years 4 months	3 years 8 months
Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 6,381	$ 720
Finite-Lived Intangible Assets, Accumulated Amortization	(848)	(264)
Finite-Lived Intangible Assets, Net	$ 5,533	$ 456
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 5 months	2 years 1 month