Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Assets:
Available-for-sale securities	$ 130,018	$ 129,722
Short-term investments	130,018	129,722
Municipal bonds and notes
Assets:
Available-for-sale securities	999	6,000
Zero coupon bonds
Assets:
Available-for-sale securities	128,489	123,192
Certificates of deposit
Assets:
Available-for-sale securities	530	530
Fair value measured on recurring basis | Municipal bonds and notes
Assets:
Available-for-sale securities	999	6,000
Fair value measured on recurring basis | Zero coupon bonds
Assets:
Available-for-sale securities	128,489	123,192
Fair value measured on recurring basis | Certificates of deposit
Assets:
Short-term investments	530	530
Fair value measured on recurring basis | Commodity swap contracts
Liabilities:
Derivative liabilities	11,034	4,383
Fair value measured on recurring basis | Embedded derivatives
Assets:
Derivative assets	11,345	6,776
Liabilities:
Derivative liabilities	32
Fair value measured on recurring basis | Level 1 | Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 1 | Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 1 | Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis | Level 1 | Commodity swap contracts
Liabilities:
Derivative liabilities	0	0
Fair value measured on recurring basis | Level 1 | Embedded derivatives
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0
Fair value measured on recurring basis | Level 2 | Municipal bonds and notes
Assets:
Available-for-sale securities	999	6,000
Fair value measured on recurring basis | Level 2 | Zero coupon bonds
Assets:
Available-for-sale securities	128,489	123,192
Fair value measured on recurring basis | Level 2 | Certificates of deposit
Assets:
Short-term investments	530	530
Fair value measured on recurring basis | Level 2 | Commodity swap contracts
Liabilities:
Derivative liabilities	0	0
Fair value measured on recurring basis | Level 2 | Embedded derivatives
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0
Fair value measured on recurring basis | Level 3 | Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 3 | Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 3 | Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis | Level 3 | Commodity swap contracts
Liabilities:
Derivative liabilities	11,034	4,383
Fair value measured on recurring basis | Level 3 | Embedded derivatives
Assets:
Derivative assets	11,345	$ 6,776
Liabilities:
Derivative liabilities	$ 32