Acquisitions (Narrative) (Details) - USD ($) $ in Thousands			3 Months Ended	12 Months Ended
	Dec. 31, 2016	Jun. 09, 2015	Dec. 31, 2016	Dec. 31, 2017	Oct. 11, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Remaining purchase adjustment	$ 2,314		$ 2,314
Goodwill	304,032		304,032			$ 292,390	$ 236,044
Nexus
Business Acquisition [Line Items]
Acquisition purchase price	$ 24,594
Working capital adjustment			$ 93
Goodwill					$ 12,283
Fair value of purchase consideration					$ 24,594
Nexus | Forecast
Business Acquisition [Line Items]
Purchase adjustment to be paid				$ 1,000
Rough Brothers Incorporated
Business Acquisition [Line Items]
Acquisition purchase price		$ 147,585
Working capital adjustment		6,302
Goodwill		57,180
Tax deductible goodwill		37,969
Indemnification assets		3,000
Fair value of purchase consideration		$ 147,585