Business Segments and Geographic Information - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	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	$ 2,341	$ 1,426	$ 4,336	$ 2,913
Investment in affiliate	0		$ 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	2,100	1,200	$ 3,700	2,300
Investment in joint venture	16,000		$ 16,000		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	200	$ 300	$ 600	$ 600
Investment in affiliate	$ 3,300		$ 3,300		$ 2,700