Commitments and Contingencies - Standby Letters of Credit, Surety Bonds and Other Commitments (Details) € in Thousands	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 11, 2020 EUR (€)
Surety Bond
Debt Instrument [Line Items]
Guarantee amount, maximum potential amount of payments	$ 17,046,000	$ 17,094,000
Cash Collateralized Letter Of Credit - Spain Tax Audits
Debt Instrument [Line Items]
Letters of credit outstanding, amount	11,300,000	11,500,000
Cash Collateralized Letter Of Credit - Spain Tax Audits, Extension of Audit
Debt Instrument [Line Items]
Letters of credit outstanding, amount	25,800,000		€ 21,600
Kendall College, St. Augustine, Walden University, and NewSchool of Architecture and Design
Debt Instrument [Line Items]
Letters of credit outstanding, amount	$ 83,600,000	$ 83,600,000