Condensed Combined Statement of Income for LLCs/LPs Accounted Under Equity Method (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity Method Investments And Joint Ventures [Abstract]
Revenues	$ 2,460	$ 2,462
Operating expenses	1,012	958
Depreciation and amortization	398	457
Interest, net	322	328
Net income	728	719
Our share of net income	$ 430	$ 429