| Components of property, plant and equipment |
The components of property, plant and equipment are as follows: | | | | | | | | | | | | | (in thousands) | March 31,
2015 | | December 31,
2014 | | March 31,
2014 | Land | $ | 23,380 |
| | $ | 23,380 |
| | $ | 21,906 |
| Land improvements and leasehold improvements | 73,651 |
| | 71,817 |
| | 67,876 |
| Buildings and storage facilities | 274,877 |
| | 275,059 |
| | 234,109 |
| Machinery and equipment | 340,109 |
| | 333,559 |
| | 309,283 |
| Software | 68,193 |
| | 55,436 |
| | 13,403 |
| Construction in progress | 18,354 |
| | 29,620 |
| | 52,200 |
| | 798,564 |
| | 788,871 |
| | 698,777 |
| Less: accumulated depreciation and amortization | 346,926 |
| | 335,264 |
| | 312,645 |
| | $ | 451,638 |
| | $ | 453,607 |
| | $ | 386,132 |
|
|
| Components of railcar assets leased to others |
The components of Rail Group assets leased to others are as follows: | | | | | | | | | | | | | (in thousands) | March 31,
2015 | | December 31,
2014 | | March 31,
2014 | Rail Group assets leased to others | $ | 402,509 |
| | $ | 384,958 |
| | $ | 316,520 |
| Less: accumulated depreciation | 89,414 |
| | 87,211 |
| | 78,986 |
| | $ | 313,095 |
| | $ | 297,747 |
| | $ | 237,534 |
|
|