Share-Based Payments And Dividends (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended			9 Months Ended			12 Months Ended		3 Months Ended			3 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended
	Nov. 04, 2011	Sep. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Maximum [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2011 Minimum [Member]	Mar. 31, 2011 Sotheby's Incentive Compensation Programs [Member]	Mar. 31, 2011 Mr. Ruprecht September 2010 Employment Agreement [Member]	Sep. 30, 2011 Restricted Stock Units [Member]	Sep. 30, 2011 Performance Share Units [Member]	Mar. 31, 2011 Performance Share Units [Member]	Sep. 30, 2011 Restricted Stock, RSU's And PSU's [Member]	Sep. 30, 2010 Restricted Stock, RSU's And PSU's [Member]	Dec. 31, 2009 Stock Option [Member]	Sep. 30, 2010 Stock Option [Member]	Sep. 30, 2011 Common Stock Transfer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefits related to share-based payment arrangements					$ 7,200,000
Unrecognized compensation expense related to the unvested portion of share-based payments		22,800,000			22,800,000
Compensation expense is expected to be amortized over a weighted-average period (years)					3.1
Restricted stock units, vesting period					4
Performance share units, employment arrangement period					4
Performance share units, employment arrangement period, renewal period					1
Stock granted during period								(4,500,000)	(3,500,000)
Granted, Shares										526,903	100,663			627,566	628,000
Vested, Shares			242,539								120,000				998,000
Grant date fair value			26,200,000							22,000,000	4,250,000
Fair value of share vested															45,200,000	18,300,000
Shares available for future awards												1,600,000
Stock option vesting period after date of grant (years)					4
Stock option expiration period after date of grant (years)					10
Aggregate intrinsic value of option exercised					3,200,000	3,200,000
Proceeds from exercise of employee stock options					2,566,000	9,980,000											4,100,000	5,900,000
Excess tax benefits realized from the exercise of stock options					800,000	1,200,000
Initial consideration (shares)					1,946,849
Percentage of initial consideration transferred back							20.00%
Common Stock transferred		147,352
Decrease in share-based payments		1,500,000			1,800,000
Percentage decrease in share-based payments		29.00%			11.00%
Share-based compensation expense		3,797,000		5,342,000	14,196,000	15,978,000							1,300,000						200,000
Share-based compensation benefit																			600,000
Dividend paid		3,400,000			6,900,000
Dividend declared per share	$ 0.08
Dividends declared	$ 5,400,000