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Debt and Financing Arrangements - Summary of Unsecured Credit Facility (Detail)
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Weighted average rates 3.08% 2.72%
Minimum [Member]    
Debt Instrument [Line Items]    
Range of effective rates 2.12% 2.19%
Maximum [Member]    
Debt Instrument [Line Items]    
Range of effective rates 5.50% 4.75%