Investments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Investments in marketable equity securities			$ 0	$ 45,000,000
Proceeds from sales of marketable equity securities			3,600,000	2,000,000
(Loss) gain on sales of marketable equity securities	0	(28,000)	879,000	477,000
Company's investments in marketable equity securities	457,969,000		457,969,000		380,087,000
Unrealized loss on investment	264,810,000		264,810,000		184,255,000
Strayer Education Inc. [Member]
Unrealized loss on investment	$ (7,000,000)		$ (7,000,000)