Condensed Combined Statement of Income for Limited Liabilities Accounted for under Equity Method (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Arlington Medical Properties
Schedule Of Equity Method Investments [Line Items]
Interest income earned on various advances made to LLCs	$ 284,000	$ 1,200,000	$ 200,000