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Revolving Credit Facilities - Additional Information (Detail)
12 Months Ended
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]  
Covenant compliance The Company was in compliance with these financial covenants at December 31, 2014.
Unsecured Debt [Member] | Revolving Credit Facility [Member]  
Debt Instrument [Line Items]  
Covenant compliance The Company was in compliance with these financial covenants at December 31, 2015 and 2014.
Unsecured Debt [Member] | Revolving Credit Facility [Member] | Prime rate [Member]  
Debt Instrument [Line Items]  
Specified spread line of credit facility 0.15%
Unsecured Debt [Member] | Revolving Credit Facility [Member] | LIBOR [Member]  
Debt Instrument [Line Items]  
Specified spread line of credit facility 1.00%
JP Morgan Securities, LLC and Wells Fargo Securities, LLC [Member] | Unsecured Debt [Member] | Revolving Credit Facility [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] | Unsecured Debt [Member] | Revolving Credit Facility [Member]  
Debt Instrument [Line Items]  
Unsecured revolving credit facility $ 50,000,000