| Accounts receivable |
Accounts receivable consist of the following at: | | | | | | | | | | | April 30, 2017 | | July 31, 2016 | Billed receivables from commercial and international customers | | $ | 69,149,000 |
| | 90,185,000 |
| Unbilled receivables from commercial and international customers | | 24,929,000 |
| | 19,333,000 |
| Billed receivables from the U.S. government and its agencies | | 16,918,000 |
| | 21,465,000 |
| Unbilled receivables from the U.S. government and its agencies | | 10,927,000 |
| | 21,013,000 |
| Total accounts receivable | | 121,923,000 |
| | 151,996,000 |
| Less allowance for doubtful accounts | | 1,475,000 |
| | 1,029,000 |
| Accounts receivable, net | | $ | 120,448,000 |
| | 150,967,000 |
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