7  Property, Plant and Equipment 8  Goodwill and Intangible Assets At December 31, 2013 and 2012, property, plant and equipment were comprised of the following: The changes in the carrying value of goodwill, all of which is included in our Enterprise Networks division, for the year ended  December 31, 2013 are as follows:  We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its  carrying amount. When evaluating whether goodwill is impaired, we compare the fair value of the reporting unit to which  the goodwill is assigned to the reporting unit’s carrying amount, including goodwill. If the carrying amount of the reporting  unit exceeds its fair value, then the amount of the impairment loss is measured. There were no impairment losses recognized  during 2013 or 2012.  Intangible assets are included in other assets in the accompanying Consolidated Balance Sheets and include intangible  assets acquired in conjunction with our acquisition of Objectworld Communications Corporation on September 15, 2009,  Bluesocket, Inc. on August 4, 2011, and the NSN BBA business on May 4, 2012. The following table presents our intangible assets as of December 31, 2013 and 2012: Amortization expense was $2.4 million, $2.0 million and $0.7 million in 2013, 2012 and 2011, respectively. Depreciation expense was $12.2 million, $12.1 million and $10.8 million in 2013, 2012 and 2011, respectively.  (In thousands)  2013 2012  Land $4,263 $4,263  Building and land improvements 21,776 20,915  Building 68,479 68,479  Furniture and fixtures 16,465 16,631  Computer hardware and software 70,468 68,596  Engineering and other equipment 104,584 99,081  Total Property, Plant and Equipment 286,035 277,965  Less accumulated depreciation (209,296) (197,719)  Total Property, Plant and Equipment, net $76,739 $80,246 (In thousands) Balance, December 31, 2012 $3,492 Acquisitions — Impairment losses — Balance, December 31, 2013 $3,492 Balance as of December 31, 2013 Goodwill $3,492 Accumulated impairment losses — Total goodwill $3,492 (In thousands) December 31, 2013 December 31, 2012 Gross Value Accumulated Amortization Net Value Gross Value Accumulated Amortization Net Value Customer relationships $6,996 $(1,555) $5,441 $6,769 $(766) $6,003 Developed technology 6,537 (2,692) 3,845 6,397 (1,354) 5,043 Intellectual property 2,340 (1,185) 1,155 2,340 (851) 1,489 Trade names 270 (145) 125 270 (85) 185 Other 14 (8) 6 13 (3) 10 Total $16,157 $(5,585) $10,572 $15,789 $(3,059) $12,730 ADTRAN 2013 Annual Report 56