Secured Debt Agreements, Net - Summary of Key Terms of Credit Facilities (Parenthetical) (Detail) - Credit Facilities [Member]	12 Months Ended
	Dec. 31, 2017 ExtensionOptions
MetLife [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes five one-year extension options which may be exercised at our sole discretion.
Number of extension options	5
Term of maturity date	1 year
Bank of America [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes two one-year extension options which may be exercised at our sole discretion.
Number of extension options	2
Term of maturity date	1 year