Investments (Narrative) (Details) (USD $)	12 Months Ended											3 Months Ended					12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Jan. 02, 2011	Dec. 31, 2012 Berkshire Hathaway Inc [Member]	Dec. 31, 2011 Berkshire Hathaway Inc [Member]	Dec. 31, 2012 Berkshire Hathaway Inc [Member] Class A Common Stock [Member]	Dec. 31, 2011 Berkshire Hathaway Inc [Member] Class A Common Stock [Member]	Dec. 31, 2012 Berkshire Hathaway Inc [Member] Class B Common Stock [Member]	Dec. 31, 2011 Berkshire Hathaway Inc [Member] Class B Common Stock [Member]	Oct. 02, 2011 Corinthian Colleges, Inc. [Member]	Apr. 03, 2011 Corinthian Colleges, Inc. [Member]	Oct. 02, 2011 Bowater Mersey Paper Company [Member]	Dec. 31, 2012 Bowater Mersey Paper Company [Member]	Dec. 31, 2012 Classified Ventures LLC [Member]	Dec. 31, 2012 Strayer Education Inc. [Member]
Proceeds from sales of marketable equity securities	$ 2,000,000
Gain on sales of marketable equity securities	500,000
Amount of time investment had been in an unrealized loss position																	almost six months
Impairment write-down on a marketable equity security	17,998,000		53,793,000		0							23,100,000	30,700,000				18,000,000
Shares held in investee company								2,214	2,214	424,250	424,250
Company's investments in marketable equity securities	380,087,000	[1]	303,201,000	[1]		334,900,000	286,400,000
Percentage of total fair value of the Company's investments in marketable equity securities						88.00%	94.00%
Equity Method Investment, Ownership Percentage																16.50%
Percentage Of Common Stock Held By Investee Company						23.00%
Percentage Of Investment Held In Investee Company						less than 1%
Available-for-sale Securities, Gross Unrealized Gains						177,600,000	129,100,000
Impairment charge on the Company's investment in affiliate														9,200,000
New investments in marketable equity securities	45,000,000		0		0
Unrealized gain on investment	$ 184,255,000		$ 133,930,000
Percentage of equity method investment ownership sold															49.00%

[1] The Company’s investments in marketable equity securities are classified as available-for-sale.