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Other long-term liabilities - Schedule of Long-Term Liabilities and Deferred Credits (Detail) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Other Long-term Liabilities |  |  |
Advances in aid of construction | $ 79,864 | $ 60,828 |
Environmental remediation obligation | 69,383 | 58,061 | $ 55,621
Asset retirement obligations | 79,968 | 53,879 | $ 43,291
Customer deposits | 31,939 | 31,946 |
Unamortized investment tax credits | 17,893 | 18,234 |
Deferred credits | 21,156 | 18,952 |
Preferred shares, Series C | 13,698 | 13,793 |
Hook up fees | 17,704 | 9,610 |
Lease liabilities | 14,288 | 9,695 |
Contingent development support obligations | 12,273 | 9,446 |
Note payable to related party | 30,493 | 0 |
Other | 23,027 | 16,896 |
Other long-term liabilities | 411,686 | 301,340 |
Less: current portion | (72,505) | (57,939) |
Other long-term liabilities, excluding current | 339,181 | 243,401 |
Transfers from advances in aid of construction to contributions in aid of construction | 1,994 | 5,465 |
Undiscounted, unescalated cost of environmental cleanup activities | 60,803 | 58,484 |
Accrual for environmental loss contingencies to be incurred over next four years | 43,995 |  |
Regulatory assets | $ 845,471 | 559,887 |
Note payable to related party |  |  |
Other Long-term Liabilities |  |  |
Interest rate (percent) | 0.675% |  |
Atlantica |  |  |
Other Long-term Liabilities |  |  |
Contingent consideration related to prior acquisition |  | 29,100 |
San Antonio Water System |  |  |
Other Long-term Liabilities |  |  |
Additional deferred credits related to investment in San Antonio Water System |  | 5,000 |
Environmental costs |  |  |
Other Long-term Liabilities |  |  |
Environmental remediation, rate recovery period | 7 years |  |
Regulatory assets | $ 87,308 | $ 82,300 |
Minimum |  |  |
Other Long-term Liabilities |  |  |
Other liability repayment period | 5 years |  |
Accrual for environmental cleanup, discount rate (percent) | 0.80% |  |
Maximum |  |  |
Other Long-term Liabilities |  |  |
Other liability repayment period | 40 years |  |
Accrual for environmental cleanup, discount rate (percent) | 3.40% |  |

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