Investment in Joint Venture - Summarized Balance Sheet Information of Unconsolidated Joint Venture (Detail) - Joint Venture [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Current assets	$ 52,856	$ 47,600
Non-current assets	33,985	24,763
Total assets	86,841	72,363
Current liabilities	38,109	26,165
Total liabilities	$ 38,109	$ 26,165