Acquisitions - AQSense, S.L. Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Aug. 30, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 113,208	$ 95,280		$ 81,448
AQSense, S.L. [Member]
Business Acquisition [Line Items]
Accounts receivable			$ 168
Goodwill			1,383
Accrued expenses			(14)
Purchase price			2,519
Customer Relationships [Member] | AQSense, S.L. [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets			598
Technology-Based Intangible Assets [Member] | AQSense, S.L. [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets			$ 384