Acquisitions (Schedule of Allocation of the Purchase Price Consideration of the Fair Value of Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Feb. 22, 2017	Dec. 31, 2016	Oct. 11, 2016	Dec. 31, 2015	Jun. 09, 2015
Business Acquisition [Line Items]
Goodwill	$ 321,074		$ 304,032		$ 292,390
Package Concierge
Business Acquisition [Line Items]
Cash		$ 590
Working capital		(1,998)
Property, plant, and equipment		55
Acquired intangible assets		3,600
Other assets		8
Deferred income taxes		(128)
Goodwill		16,790
Fair value of purchase consideration		$ 18,917
Nexus
Business Acquisition [Line Items]
Cash				$ 2,495
Working capital				(1,109)
Property, plant, and equipment				4,702
Acquired intangible assets				6,200
Other assets				23
Goodwill				11,451
Fair value of purchase consideration				$ 23,762
Rough Brothers Incorporated
Business Acquisition [Line Items]
Cash						$ 4,651
Working capital						21,436
Property, plant, and equipment						12,797
Acquired intangible assets						56,392
Other assets						3,049
Deferred income taxes						(4,892)
Other liabilities						(3,028)
Goodwill						57,180
Fair value of purchase consideration						$ 147,585