Investments and Fair Value Measurements - Investment Category and Length (Details) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2021 USD ($) company	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) company
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	$ 6,175			$ 6,175		$ 2,048
Gross unrealized loss, in loss position less than twelve months	(11)			(11)		(2)
Fair value, total in loss position	6,175			6,175		2,048
Gross unrealized loss, total in loss position	(11)			(11)		(2)
Minority Investments
Investments, equity method	9,340			$ 9,340		$ 6,376
Number of equity method investments | company				5		5
Impairment charge	0	$ 0	$ 1,100	$ 0	$ 0
Certificates of deposit.
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	959			959
Gross unrealized loss, in loss position less than twelve months	(1)			(1)
Fair value, total in loss position	959			959
Gross unrealized loss, total in loss position	(1)			(1)
Corporate bonds
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	5,216			5,216		$ 2,048
Gross unrealized loss, in loss position less than twelve months	(10)			(10)		(2)
Fair value, total in loss position	5,216			5,216		2,048
Gross unrealized loss, total in loss position	(10)			(10)		(2)
Other assets
Minority Investments
Investments, equity method	$ 9,300			$ 9,300		$ 6,400