Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 83,830		$ 83,830
Finite-Lived Intangible Assets, Accumulated Amortization	(51,940)		(42,115)
Finite-Lived Intangible Assets, Net	31,890		41,715
Value of Business Acquired
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	42,788		42,788
Finite-Lived Intangible Assets, Accumulated Amortization	(42,788)		(34,335)
Finite-Lived Intangible Assets, Net	0		8,453
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	34,661		34,661
Finite-Lived Intangible Assets, Accumulated Amortization	(7,793)		(6,669)
Finite-Lived Intangible Assets, Net	$ 26,868		27,992
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years 10 months	8 years
Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 6,381		6,381
Finite-Lived Intangible Assets, Accumulated Amortization	(1,359)		(1,111)
Finite-Lived Intangible Assets, Net	$ 5,022		$ 5,270
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years 10 months	6 years