Acquisitions - GVi Ventures, Inc. Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Apr. 12, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 113,208		$ 95,280	$ 81,448
GVi Ventures, Inc. [Member]
Business Acquisition [Line Items]
Accounts receivable		$ 423
Inventories		120
Prepaid expenses and other current assets		1
Accounts payable		(152)
Accrued expenses		(10)
Goodwill		1,476
Purchase price		5,368
Technology-Based Intangible Assets [Member] | GVi Ventures, Inc. [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		910
Customer Relationships [Member] | GVi Ventures, Inc. [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 2,600