Accounts Receivable - Summary of Accounts Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contract receivables	$ 60,543	$ 72,835
Allowance for doubtful accounts	(4,156)	(1,749)
Total accounts receivable	67,990	83,062
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade receivables	$ 11,603	$ 11,976