Condensed Combined Statement of Income for LLCs/LPs Accounted Under Equity Method (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity Method Investments And Joint Ventures [Abstract]
Revenues	$ 2,441	$ 2,343	$ 7,432	$ 7,256
Operating expenses	927	938	2,933	2,873
Depreciation and amortization	434	436	1,317	1,331
Interest, net	325	329	969	985
Net income	755	640	2,213	2,067
Our share of net income	$ 453	$ 351	$ 1,337	$ 1,205