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Revolving Credit Facilities - Additional Information (Detail) - Unsecured Debt [Member] - Revolving Credit Facility [Member]
6 Months Ended
Jun. 30, 2017
USD ($)
Debt Instrument [Line Items]  
Covenant compliance The Company was in compliance with these financial covenants at June 30, 2017.
LIBOR [Member]  
Debt Instrument [Line Items]  
Specified spread line of credit facility 1.00%
JP Morgan Securities, LLC and Wells Fargo Securities, LLC [Member]  
Debt Instrument [Line Items]  
Unsecured revolving credit facility borrowing capacity $ 750,000,000
Accordion feature $ 1,250,000,000
Line of credit facility competitive bid option on periodic interest rates up to 50% of the facility
Facility fee 0.20%
Revolving credit facility maturity extension option two six-month options to extend the maturity to June 2020 upon the Company’s request
PNC Bank National Association [Member]  
Debt Instrument [Line Items]  
Unsecured revolving credit facility $ 50,000,000