Accounts Receivable - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Amount billed but not received under retainage provisions in contracts	$ 2,500	$ 3,200
Retainage receivables on contracts minimum period	1 year
Retainage receivables on contracts maximum period	2 years
Provision for doubtful accounts	$ 3,895	848	$ 702
Charge-offs	$ 1,500	$ 300	$ 200