Acquisitions (Schedule of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands				12 Months Ended
	Feb. 22, 2017	Oct. 11, 2016	Jun. 09, 2015	Dec. 31, 2017
Package Concierge
Business Acquisition [Line Items]
Fair Value	$ 3,600
Package Concierge | Trademarks
Business Acquisition [Line Items]
Fair Value	600
Package Concierge | Technology
Business Acquisition [Line Items]
Fair Value	$ 1,300
Estimated Useful Life	10 years
Package Concierge | Customer relationships
Business Acquisition [Line Items]
Fair Value	$ 1,700
Estimated Useful Life	7 years
Nexus
Business Acquisition [Line Items]
Fair Value		$ 6,200
Estimated Useful Life				3 months
Nexus | Trademarks
Business Acquisition [Line Items]
Fair Value		3,200
Nexus | Technology
Business Acquisition [Line Items]
Fair Value		1,300
Estimated Useful Life				15 years
Nexus | Customer relationships
Business Acquisition [Line Items]
Fair Value		800
Estimated Useful Life				11 years
Nexus | Backlog
Business Acquisition [Line Items]
Fair Value		$ 900
Rough Brothers Incorporated
Business Acquisition [Line Items]
Fair Value			$ 56,392
Rough Brothers Incorporated | Trademarks
Business Acquisition [Line Items]
Fair Value			13,550
Rough Brothers Incorporated | Technology
Business Acquisition [Line Items]
Fair Value			3,550
Rough Brothers Incorporated | Customer relationships
Business Acquisition [Line Items]
Fair Value			32,892
Rough Brothers Incorporated | Non-compete agreements
Business Acquisition [Line Items]
Fair Value			1,300
Rough Brothers Incorporated | Backlog
Business Acquisition [Line Items]
Fair Value			$ 5,100
Rough Brothers Incorporated | Maximum | Technology
Business Acquisition [Line Items]
Estimated Useful Life			15 years
Rough Brothers Incorporated | Maximum | Customer relationships
Business Acquisition [Line Items]
Estimated Useful Life			17 years
Rough Brothers Incorporated | Minimum | Technology
Business Acquisition [Line Items]
Estimated Useful Life			7 years
Rough Brothers Incorporated | Minimum | Customer relationships
Business Acquisition [Line Items]
Estimated Useful Life			11 years
Rough Brothers Incorporated | Minimum | Non-compete agreements
Business Acquisition [Line Items]
Estimated Useful Life			5 years
Rough Brothers Incorporated | Minimum | Backlog
Business Acquisition [Line Items]
Estimated Useful Life			6 months