Significant Accounting Policies - Goodwill and Indefinite-lived Intangible Assets (Details) - USD ($)		12 Months Ended
	Sep. 01, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Nov. 01, 2013
Business Acquisition [Line Items]
Goodwill acquired		$ 217,203,000
Goodwill		243,486,000	$ 26,563,000	$ 26,563,000
Impairment of goodwill		0	0	7,336,000
HCN
Business Acquisition [Line Items]
Goodwill acquired		0
Identified intangible assets with indefinite useful life		3,721,000
Finite lived intangible assets gross		4,361,000
Goodwill		26,563,000	26,563,000	26,563,000
Impairment of goodwill		0	0	7,300,000
Fair value exceeding carrying value		$ 20,100,000
Fair value exceeding carrying value (in percent)		51.80%
Rasmussen
Business Acquisition [Line Items]
Goodwill acquired	$ 217,200,000
Identified intangible assets with indefinite useful life	51,000,000
Finite lived intangible assets gross	35,500,000
Goodwill	$ 216,923,000	$ 217,200,000
Indefinite-lived intangible assets acquired			51,000,000
HCN
Business Acquisition [Line Items]
Goodwill		26,600,000	38,600,000
Indefinite-lived intangible assets acquired		$ 3,700,000			$ 3,700,000
Impairment of goodwill			$ 0	$ 7,300,000