Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Income from continuing operations	$ 14,162	$ 13,032
Income from discontinued operations, net of income attributable to the noncontrolling interest	0	6,450
Net income attributable to Alexander's	$ 14,162	$ 19,482
Weighted average shares outstanding - basic and diluted (in shares)	5,108,016	5,106,984
Income from continuing operations (in dollars per share)	$ 2.77	$ 2.55
Income from discontinued operations, net (in dollars per share)	$ 0	$ 1.26
Net income per common share (in dollars per share)	$ 2.77	$ 3.81