Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Future Minimum Rental Payments Due under Terms of Leases (Detail)

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Commitments and Contingencies - Future Minimum Rental Payments Due under Terms of Leases (Detail) (USD $)
In Thousands, unless otherwise specified
 9 Months Ended
Sep. 30, 2013
Operating Leased Assets [Line Items]  
For the three months ending December 31, 2013 $ 14,727
For the year ended December 31, 2014 59,940
For the year ended December 31, 2015 59,267
For the year ended December 31, 2016 56,272
For the year ended December 31, 2017 54,641
For the year ended December 31, 2018 52,850
Thereafter 279,421
Ground Leases [Member]
  
Operating Leased Assets [Line Items]  
For the three months ending December 31, 2013 103
For the year ended December 31, 2014 413
For the year ended December 31, 2015 413
For the year ended December 31, 2016 413
For the year ended December 31, 2017 416
For the year ended December 31, 2018 417
Thereafter 4,919
Ground Leases [Member] | Tulsa, OK [Member]
  
Operating Leased Assets [Line Items]  
Lease End Date 2021-04
For the three months ending December 31, 2013 38
For the year ended December 31, 2014 153
For the year ended December 31, 2015 153
For the year ended December 31, 2016 153
For the year ended December 31, 2017 153
For the year ended December 31, 2018 153
Thereafter 381
Ground Leases [Member] | Dartmouth, MA [Member]
  
Operating Leased Assets [Line Items]  
Lease End Date 2036-05
For the three months ending December 31, 2013 44
For the year ended December 31, 2014 174
For the year ended December 31, 2015 174
For the year ended December 31, 2016 174
For the year ended December 31, 2017 174
For the year ended December 31, 2018 174
Thereafter 3,474
Ground Leases [Member] | Springfield, MA [Member]
  
Operating Leased Assets [Line Items]  
Lease End Date 2030-02
For the three months ending December 31, 2013 21
For the year ended December 31, 2014 86
For the year ended December 31, 2015 86
For the year ended December 31, 2016 86
For the year ended December 31, 2017 89
For the year ended December 31, 2018 90
Thereafter $ 1,064