Investment in Joint Venture - Summarized Activity Related to Investment in Joint Venture (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Beginning Balance	$ 36,008
Our share of cumulative earnings	5,211	$ 5,938	$ 5,001
Ending Balance	39,822	36,008
Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Beginning Balance	36,008
Our share of cumulative earnings	5,582
Dividends declared and paid by joint venture	(4,156)
Accretion of basis difference from purchase accounting	(371)
Foreign currency translation gain	2,759
Ending Balance	$ 39,822	$ 36,008