Business Segments and Geographic Information - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of reportable business segments | segment	4
Equity in earnings of affiliates, net of income tax provision	$ 1,995	$ 1,487
Investment in affiliate	$ 0		$ 0
SACS
Schedule of Equity Method Investments [Line Items]
Ownership percentage in entity	50.00%
Equity in earnings of affiliates, net of income tax provision	$ 1,600	1,100
Investment in joint venture	$ 19,900		18,100
Geo Amey
Schedule of Equity Method Investments [Line Items]
Ownership percentage in entity	50.00%
Equity in earnings of affiliates, net of income tax provision	$ 400	$ 300
Investment in affiliate	$ 3,300		$ 2,700