Financial Instruments and Fair Value Measurements - Carrying Amount and Fair Value (Details) - Nonrecurring - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Carrying Value
Financial instruments and fair value measurements
Debt	$ 459,221	$ 391,411
Fair Value
Financial instruments and fair value measurements
Debt	412,259	369,127
Level 1 | Carrying Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,824	4,486
Level 1 | Fair Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,750	4,361
Level 2 | Carrying Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	262,484	194,525
Level 2 | Carrying Value | Variable rate debt
Financial instruments and fair value measurements
Debt	196,737	196,886
Level 2 | Fair Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	215,522	172,241
Level 2 | Fair Value | Variable rate debt
Financial instruments and fair value measurements
Debt	196,737	196,886
Level 3 | Carrying Value
Financial instruments and fair value measurements
Senior Notes held by SPE	178,162	177,857
Level 3 | Carrying Value | Time deposit
Financial instruments and fair value measurements
Investments held by SPEs	200,000	200,000
Level 3 | Fair Value
Financial instruments and fair value measurements
Senior Notes held by SPE	181,286	179,564
Level 3 | Fair Value | Time deposit
Financial instruments and fair value measurements
Investments held by SPEs	$ 200,000	$ 200,000