Acquisitions (Narrative) (Details) - USD ($) $ in Thousands				3 Months Ended	12 Months Ended
	Feb. 22, 2017	Dec. 31, 2016	Jun. 09, 2015	Mar. 31, 2017	Dec. 31, 2017	Oct. 11, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 304,032			$ 321,074		$ 292,390
Adjustments to prior year acquisitions					$ (832)
Package Concierge
Business Acquisition [Line Items]
Acquisition purchase price	$ 18,900
Goodwill	16,790
Fair value of purchase consideration	$ 18,917
Nexus
Business Acquisition [Line Items]
Acquisition purchase price		23,800
Goodwill						$ 11,451
Purchase adjustment to be paid		$ 1,000
Working capital adjustment				$ 200
Adjustments to prior year acquisitions				$ 800
Fair value of purchase consideration						$ 23,762
Rough Brothers Incorporated
Business Acquisition [Line Items]
Acquisition purchase price			$ 147,600
Goodwill			57,180
Tax deductible goodwill			38,000
Indemnification assets			3,000
Fair value of purchase consideration			$ 147,585