| Property, Plant and Equipment, Net |
| | | 7. | Property, Plant and Equipment, Net |
| | | | | | | | | | As of December 31, | | 2015 | | 2014 | Plant, machinery, furniture and fixtures | $ | 305,763 |
| | $ | 293,080 |
| Building and leasehold improvements | 14,698 |
| | 14,565 |
| Land and land improvements | 60,687 |
| | 60,395 |
| Construction in progress | 6,660 |
| | 3,238 |
| Property, plant and equipment, gross | 387,808 |
| | 371,278 |
| Less: accumulated depreciation | (136,899 | ) | | (121,152 | ) | Property, plant and equipment, net | $ | 250,909 |
| | $ | 250,126 |
|
Depreciation expense for the years ended December 31, 2015, 2014 and 2013 was $15.9 million, $14.5 million and $13.8 million, respectively. Property, plant and equipment include the following amounts for capital leases: | | | | | | | | | | As of December 31, | | 2015 | | 2014 | Plant, machinery, furniture and fixtures | $ | 16,457 |
| | $ | 16,931 |
| Building and leasehold improvements | 4,719 |
| | 4,719 |
| Land and land improvements | 251 |
| | 251 |
| Property, plant and equipment, gross | 21,427 |
| | 21,901 |
| Less: accumulated amortization | (9,572 | ) | | (8,175 | ) | Property, plant and equipment, net | $ | 11,855 |
| | $ | 13,726 |
|
Amortization expense on capital leased assets for the years ended December 31, 2015, 2014 and 2013 was $1.4 million, $1.3 million and $1.3 million, respectively. |