Fair Value Disclosures - Financial instruments measured at fair value on recurring basis (Details) - Fair value on a recurring basis - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Equity securities	$ 197	$ 132
Investments measured at net asset value	31,738	32,039
Level 1
Assets:
Equity securities	197	132
Level 2
Assets:
Equity securities	0	0
Level 3
Assets:
Equity securities	$ 0	$ 0