Notes Receivable Backed by Real Estate - Summary of Notes Receivable Backed by Real Estate (Detail) - USD ($) $ in Thousands					12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Loans And Leases Receivable [Line Items]
Beginning Balance					$ 32,100		$ 235,050
Additions					53,796	[1]	0
Repayments					(32,100)		(202,950)	$ (9,866)
Assumption by USLF	[1]				(19,536)
Ending Balance		$ 34,260	$ 32,100	$ 235,050	$ 34,260		$ 32,100	$ 235,050
Interest Rates		3.50%
Maturity Dates		2018-03
Minimum [Member]
Loans And Leases Receivable [Line Items]
Interest Rates			5.80%	2.00%
Maturity Dates			2017-04	2016-02
Maximum [Member]
Loans And Leases Receivable [Line Items]
Interest Rates			10.00%	10.00%
Maturity Dates			2017-12	2017-04

[1] In 2017, we received a note receivable backed by real estate through a property disposition. Subsequently, this note was assumed through the contribution of operating properties to USLF.