Investments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended			0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Mar. 31, 2014 Corinthian Colleges, Inc. [Member]	Oct. 01, 2014 Classified Ventures LLC [Member] Subsequent Event [Member]	Dec. 31, 2014 Classified Ventures LLC [Member] Subsequent Event [Member] Scenario, Forecast [Member]	Jun. 30, 2014 Classified Ventures' sale of apartments.com [Member]	Apr. 01, 2014 Classified Ventures' sale of apartments.com [Member]	Jun. 30, 2014 Berkshire Exchange Transaction [Member] Berkshire Hathaway Inc [Member]	Jun. 30, 2014 Berkshire Exchange Transaction [Member] Berkshire Hathaway Inc [Member] Common Class A [Member]	Jun. 30, 2014 Berkshire Exchange Transaction [Member] Berkshire Hathaway Inc [Member] Common Class B [Member]
Schedule of Investments [Line Items]
Number of Berkshire Shares Exchanged														2,107	1,278
Gain on Berkshire marketable equity securities exchange	$ 0	$ 0	$ 266,733,000	$ 0									$ 266,700,000
Gain on exchange of Berkshire Hathaway shares	0	0	(3,044,000)	879,000
Impairment write-down on a marketable equity security								500,000
Proceeds from sales of marketable equity securities			5,800,000	3,600,000
(Loss) gain on sales of marketable equity securities			(2,600,000)	900,000
New investments in marketable equity securities			0	0
Investments in commercial paper	50,000,000		50,000,000		0
Cash distribution from equity method investment												95,000,000
Investment maturity length for commercial paper						3 months 1 day	6 months
Pre-tax gain on equity method investments	4,613,000	5,892,000	100,168,000	13,178,000							90,900,000
Company's investments in marketable equity securities	127,270,000		127,270,000		487,156,000
Unrealized loss on investment	70,303,000		70,303,000		289,438,000
Proceeds from sale of equity method investment									408,500,000
Amount of cash proceeds held in escrow									16,500,000
Pre-tax gain on sale of equity method investment										$ 393,000,000