Year Ended December 31, 2012 2011 2010 Wholly-Owned Properties Rental revenues $ 449,657 $ 346,764 $ 284,163 Interest and other income 44 66 41 Total revenues from external customers 449,701 346,830 284,204 Operating expenses before depreciation, amortization, ground/facility lease, and allocation of corporate overhead (210,980 ) (164,508 ) (133,904 ) Ground/facility leases (2,148 ) (1,329 ) (1,103 ) Interest expense (34,683 ) (35,904 ) (45,984 ) Operating income before depreciation, amortization and allocation of corporate overhead $ 201,890 $ 145,089 $ 103,213 Depreciation and amortization $ 109,590 $ 80,441 $ 66,197 Capital expenditures $ 375,539 $ 225,852 $ 75,249 Total segment assets at December 31, $ 4,958,314 $ 2,843,749 $ 2,522,690 On-Campus Participating Properties Rental revenues $ 26,166 $ 25,252 $ 23,975 Interest and other income 16 15 18 Total revenues from external customers 26,182 25,267 23,993 Operating expenses before depreciation, amortization, ground/facility lease, and allocation of corporate overhead (10,367 ) (9,437 ) (9,811 ) Ground/facility lease (2,100 ) (2,279 ) (1,841 ) Interest expense (5,671 ) (5,840 ) (6,006 ) Operating income before depreciation, amortization and allocation of corporate overhead $ 8,044 $ 7,711 $ 6,335 Depreciation and amortization $ 4,644 $ 4,469 $ 4,345 Capital expenditures $ 2,141 $ 1,832 $ 1,141 Total segment assets at December 31, $ 72,922 $ 73,109 $ 75,948 Development Services Development and construction management fees $ 8,574 $ 7,497 $ 9,302 Operating expenses (10,739 ) (9,820 ) (9,367 ) Operating loss before depreciation, amortization and allocation of corporate overhead $ (2,165 ) $ (2,323 ) $ (65 ) Total segment assets at December 31, $ 1,804 $ 14,159 $ 4,757 Property Management Services Property management fees from external customers $ 6,893 $ 7,254 $ 8,670 Intersegment revenues 16,349 13,867 11,558 Total revenues 23,242 21,121 20,228 Operating expenses (10,098 ) (9,532 ) (7,842 ) Operating income before depreciation, amortization and allocation of cor