Marketable Securities - Available-for-sale Securities by Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Summary of maturities, at par, of marketable securities
Year one	$ 10,180	$ 2,751
Year two	750
Total	10,930	2,751
Certificates of deposit
Summary of maturities, at par, of marketable securities
Year one	400
Year two	0
Total	400
U.S. Treasury and agency notes
Summary of maturities, at par, of marketable securities
Year one	855	801
Year two	500
Total	1,355	801
Corporate notes
Summary of maturities, at par, of marketable securities
Year one	8,925	1,950
Year two	250
Total	$ 9,175	$ 1,950