Annual report pursuant to Section 13 and 15(d)

Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Real Estate (Detail)

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Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Real Estate (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]      
Balance at beginning of period $ 642,353us-gaap_RealEstateGrossAtCarryingValue $ 533,753us-gaap_RealEstateGrossAtCarryingValue $ 442,521us-gaap_RealEstateGrossAtCarryingValue
Additions:      
Acquisitions during period 105,813us-gaap_RealEstateOtherAcquisitions 103,424us-gaap_RealEstateOtherAcquisitions 85,462us-gaap_RealEstateOtherAcquisitions
Improvements 13,889us-gaap_RealEstateImprovements 5,176us-gaap_RealEstateImprovements 5,770us-gaap_RealEstateImprovements
Deductions:      
Dispositions during period (39,490)us-gaap_RealEstateCostOfRealEstateSold    
Balance at end of period $ 722,565us-gaap_RealEstateGrossAtCarryingValue $ 642,353us-gaap_RealEstateGrossAtCarryingValue $ 533,753us-gaap_RealEstateGrossAtCarryingValue