Business Segments and Geographic Information - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)	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	$ 2,735	$ 1,342	$ 7,071	$ 4,255
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	2,200	1,100	$ 5,900	3,400
Investment in joint venture	12,800		$ 12,800		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	600	$ 200	$ 1,200	$ 800
Investment in affiliate	$ 3,900		$ 3,900		$ 2,700