Income Taxes (Schedule Of Tax Effects Of Principal Temporary Differences That Give Rise To Deferred Tax Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Tuition receivable	$ 4,629	$ 3,130
Employee-related liabilities	420	601
Deferred gain on sale of property	111	111
Unrealized gains on marketable securities		186
Current net deferred tax asset	5,160	4,028
Property and equipment	(15,335)	(5,631)
Deferred leasing costs	4,130	3,013
Stock-based compensation	13,656	10,369
Deferred gain on sale of property	495	606
Interest rate swap	399
Other	(19)	17
Long-term net deferred tax asset	3,326	8,374
Net deferred tax asset	$ 8,486	$ 12,402