Lease Commitments - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Operating Leased Assets [Line Items]
Number of ground/facility and office space lease agreements | agreement	49
Operating Lease, Weighted Average Discount Rate, Percent	5.35%
Operating Lease, Weighted Average Remaining Lease Term	62 years 4 months 24 days
Minimum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	7 years
Maximum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	102 years
Student Lease Property [Member]
Operating Leased Assets [Line Items]
Operating Lease, Lease Income	$ 852.0	$ 794.7	$ 711.3
Commercial Lease Property [Member]
Operating Leased Assets [Line Items]
Operating Lease, Lease Income	$ 13.2	$ 13.1	$ 12.8
On-Campus Participating Properties
Operating Leased Assets [Line Items]
Percentage of net cash flow receivable per agreement	50.00%