12 . Commitments and Contingencies At March 31, 2018 , we had 14 outstanding letter of credit obligations totaling $158,969,000 and expiring between 2018 and 2024 . At March 31, 2018 , we had outstanding construction in progress of $ 180,984,000 and were committed to providing additional funds of approximately $ 392,710,000 to complete construction. At March 31, 2018 , we had contingent purchase obligations totaling $ 10,350,000 . These contingent purchase obligations relate to unfunded capital improvement obligation s and contingent obligations on acquisitions. Rents due from the tenant are increased to reflect the additio nal investment in the property. We evaluate our leases for operating versus capital lease treatment in accordance with 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 n et 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 March 31, 2018 , we had operating lease obligations o f $ 1,121,736,000 relating to certain ground leases and company office space and capital lease obligations of $ 87,922,000 relating primarily to certain investment properties. 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 March 31, 2018 , aggregate future minimum rentals to be received under these noncancelable subleases totaled $ 76,388,000 .