Condensed Combined Statement of Income for Limited Liabilities Accounted for under Equity Method (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investments And Joint Ventures [Abstract]
Revenues		$ 10,673	$ 15,252	$ 14,347
Operating expenses		3,883	5,439	5,605
Depreciation and amortization		1,988	2,554	2,398
Interest, net		1,570	2,565	2,578
Net income		3,232	4,694	3,766
Our share of net income	[1]	$ 2,416	$ 4,456	$ 2,536

[1] Our share of net income during 2017, 2016 and 2015, includes approximately $284,000, $1.2 million and $200,000, respectively, of interest income earned by us on an advance made to Arlington Medical Properties, LLC.