Fair Value Measurements - Schedule of fair value of assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Assets measured at fair value	$ 31,356	$ 27,119
Mutual Funds
Assets
Mutual funds and money market funds, fair value	28,520	24,927
Money Market Funds
Assets
Mutual funds and money market funds, fair value	2,836	2,192
Fair Value, Level 1
Assets
Assets measured at fair value	28,520	24,927
Fair Value, Level 1 | Mutual Funds
Assets
Mutual funds and money market funds, fair value	28,520	24,927
Fair Value, Level 1 | Money Market Funds
Assets
Mutual funds and money market funds, fair value	0	0
Fair Value, Level 2
Assets
Assets measured at fair value	2,836	2,192
Fair Value, Level 2 | Mutual Funds
Assets
Mutual funds and money market funds, fair value	0	0
Fair Value, Level 2 | Money Market Funds
Assets
Mutual funds and money market funds, fair value	2,836	2,192
Fair Value, Level 3
Assets
Assets measured at fair value	0	0
Fair Value, Level 3 | Mutual Funds
Assets
Mutual funds and money market funds, fair value	0	0
Fair Value, Level 3 | Money Market Funds
Assets
Mutual funds and money market funds, fair value	$ 0	$ 0