Financial Instruments and Fair Value Measurements - Carrying Amount and Fair Value (Details) - Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Carrying Value
Financial instruments and fair value measurements
Debt	$ 458,864	$ 391,411
Fair Value
Financial instruments and fair value measurements
Debt	401,769	369,127
Level 1 | Carrying Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,795	4,486
Level 1 | Fair Value | U.S. Treasury Bills
Financial instruments and fair value measurements
Investments held by SPEs	3,640	4,361
Level 2 | Carrying Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	262,541	194,525
Level 2 | Carrying Value | Variable rate debt
Financial instruments and fair value measurements
Debt	196,323	196,886
Level 2 | Fair Value | Fixed-rate debt
Financial instruments and fair value measurements
Debt	205,446	172,241
Level 2 | Fair Value | Variable rate debt
Financial instruments and fair value measurements
Debt	196,323	196,886
Level 3 | Carrying Value
Financial instruments and fair value measurements
Senior Notes held by SPE	178,085	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	175,195	179,564
Level 3 | Fair Value | Time deposit
Financial instruments and fair value measurements
Investments held by SPEs	$ 200,000	$ 200,000