12 . Commitments and Contingencies At September 30, 2012 , we had nine outstanding letter of credi t obligations totaling $ 7,172 ,000 and expiring between 201 3 and 201 4 . At September 30, 2012 , we had outstanding construction in process of $ 219,705,000 for leased properties and were committed to providing additional funds of approximately $ 217,015,000 to complete construction. At September 30, 2012 , we had contingent purchase obligations totaling $ 76,933,000 . These contingent purchase obligations relate to unfunded capital improvement obligations and contingent obligations on acquisitions . Rents due from the tenant are increased to reflect the additional investment in the property. We evaluate our leases for operating versus capital lease treatment in accordance with Accounting Standards Codification (  ASC  ) Topic 840  Leases.  A lease is classified as a capital lease if it provides for transfer of ownership of the leased asset at the end of the lease term, contains a bargain purchase option, has a lease term greater than 75% of the economic life of the leased asset, or if the net present value of the future minimum lease payments are in excess of 90% of the fair value of the leased asset. Certain leases contain bargain purchase options and have been classified as capital leases. At September 30, 2012 , we had operating lease obligations of $ 528,685,000 relating to certain ground lea ses and company office space and capital lease obligations of $88,143,000 relating to certain investment properties . We incurred rental expense relating to company office space of $ 3 30 ,000 and $ 931 ,000 for the three months and nine months ended September 30, 2012 , respectively, as compared to $ 341 , 000 and $1, 472 ,000 for the same period s in 201 1 . Regarding ground leases, we have sublease agreements with certain of our operators that require the operators to reimburse us for our monthly operating lease obligations. At September 30, 2012 , aggregate future minimum rentals to be received under these noncancela