Schedule of Accrued Cost and Expenses (Parenthetical) (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Schedule Of Accrued Liabilities [Line Items]
Commissions payable	[1]	$ 1,877	$ 1,990
Sonatide joint venture
Schedule Of Accrued Liabilities [Line Items]
Commissions payable		$ 25,900	$ 28,000

[1] Excludes $25.9 million and $28.0 million of commissions due to Sonatide at September 30, 2019 and December 31, 2018, respectively. These amounts are included in amounts due to affiliate.