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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2023
Income Taxes |
Schedule of provision for income taxes | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(in thousands) |  | 2023 |  | 2022 |  | 2021
Current tax provision: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. federal | ​ | $ | — | ​ | $ | — | ​ | $ | (1)
State | ​ |  | 1,591 | ​ |  | 1,064 | ​ |  | 366
Total current | ​ | ​ | 1,591 | ​ | ​ | 1,064 | ​ | ​ | 365
Deferred tax provision: | ​ | ​ |  | ​ | ​ |  | ​ | ​ |
U.S. federal | ​ | ​ | 32,928 | ​ | ​ | 14,320 | ​ | ​ | 8,800
State | ​ |  | 2,730 | ​ |  | 909 | ​ |  | 1,579
Total deferred | ​ | ​ | 35,658 | ​ | ​ | 15,229 | ​ | ​ | 10,379
Provision for income taxes | ​ | $ | 37,249 | ​ | $ | 16,293 | ​ | $ | 10,744
Reconciliation of effective tax rates to the U.S. statutory rate | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(in thousands) | ​ | 2023 |  | 2022 |  | 2021
Income taxes at U.S. federal statutory rate |  | $ | 29,872 |  | $ | 12,724 |  | $ | 8,182
Net state income taxes | ​ |  | 3,614 | ​ |  | 1,795 | ​ |  | 1,374
Tax credits | ​ |  | — | ​ |  | (26) | ​ |  | (720)
Unrecognized tax benefits (1) | ​ |  | 118 | ​ |  | 17 | ​ |  | 598
Valuation allowances and write off of tax attributes (2) | ​ |  | 570 | ​ |  | (68) | ​ |  | (167)
Executive compensation limitation | ​ |  | 3,470 | ​ |  | 1,901 | ​ |  | 1,559
Stock | ​ |  | (213) | ​ |  | 152 | ​ |  | 162
Other | ​ |  | (182) | ​ |  | (202) | ​ |  | (244)
Provision for income taxes | ​ | $ | 37,249 | ​ | $ | 16,293 | ​ | $ | 10,744
(1) | Includes the expiration of statute of limitations. See “Unrecognized Tax Benefits” below for further details.
(2) | See “Tax Attributes and Valuation Allowances” below for further details.
Schedule of deferred income tax balances | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31,
(in thousands) | ​ | 2023 | ​ | 2022
Deferred tax assets: |  | ​ |  |  | ​ |
Net operating loss carryforwards | ​ | $ | 164,972 | ​ | $ | 191,916
Interest expense limitation carryforward | ​ |  | 30,343 | ​ |  | 19,327
Basis difference in unconsolidated affiliate | ​ | ​ | 686 | ​ | ​ | —
Accrued liabilities | ​ |  | 6,704 | ​ |  | 4,979
Other | ​ |  | 12,015 | ​ |  | 12,834
​ | ​ | ​ | 214,720 | ​ | ​ | 229,056
Valuation allowances (1) | ​ |  | (1,177) | ​ |  | (607)
Total deferred tax assets | ​ | ​ | 213,543 | ​ | ​ | 228,449
​ | ​ | ​ | ​ | ​ | ​ | ​
Deferred tax liabilities: | ​ |  |  | ​ |  |
Property, plant and equipment | ​ | ​ | (12,125) | ​ | ​ | (8,386)
Basis difference in partnership | ​ |  | (197,999) | ​ |  | (181,377)
Other | ​ |  | (5,148) | ​ |  | (6,187)
Total deferred tax liabilities | ​ |  | (215,272) | ​ |  | (195,950)
​ | ​ | ​ | ​ | ​ | ​ | ​
Net deferred tax asset (liability) (2) | ​ | $ | (1,729) | ​ | $ | 32,499
(1) | See “Tax Attributes and Valuation Allowances” below for further details.
(2) | The 2023 and 2022 net deferred tax asset or liability are reflected in our consolidated balance sheets as deferred tax assets of $3.2 million and $33.4 million, respectively, and deferred tax liabilities of $4.9 million and $0.9 million, respectively.
Schedule of changes in valuation allowance | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(in thousands) | ​ | 2023 |  | 2022 |  | 2021
Balance at beginning of period |  | $ | (607) |  | $ | (735) |  | $ | (1,027)
Additions to valuation allowance | ​ | ​ | (742) | ​ | ​ | (88) | ​ | ​ | —
Reductions to valuation allowance | ​ | ​ | 172 | ​ | ​ | 216 | ​ | ​ | 292
Balance at end of period | ​ | $ | (1,177) | ​ | $ | (607) | ​ | $ | (735)
Schedule of changes in unrecognized tax benefits | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
(in thousands) | ​ | 2023 |  | 2022 |  | 2021
Beginning balance |  | $ | 19,651 |  | $ | 19,594 |  | $ | 18,892
Additions based on tax positions related to current year | ​ |  | 1,886 | ​ |  | 2,151 | ​ |  | 2,246
Additions based on tax positions related to prior years | ​ |  | — | ​ |  | 6 | ​ |  | 632
Reductions based on tax positions related to prior years | ​ |  | (7) | ​ |  | (105) | ​ |  | (138)
Reductions based on lapse of statute of limitations | ​ |  | (2,065) | ​ |  | (1,995) | ​ |  | (2,038)
Ending balance | ​ | $ | 19,465 | ​ | $ | 19,651 | ​ | $ | 19,594

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