Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Income from continuing operations									$ 54,663	$ 50,041	$ 54,831
Income from discontinued operations, net of income attributable to the noncontrolling interest									2,252	624,346	24,592
Net income attributable to Alexander's	$ 15,790	$ 13,824	$ 13,139	$ 14,162	$ 617,157	$ 18,856	$ 18,892	$ 19,482	$ 56,915	$ 674,387	$ 79,423
Weighted average shares outstanding - (in shares)									5,109,055	5,107,610	5,106,568
Income from continuing operations- (in dollars per share)									$ 10.70	$ 9.80	$ 10.74
Income from discontinued operations, net - (in dollars per share)									$ 0.44	$ 122.24	$ 4.81
Net income per common share (in dollars per share)									$ 11.14	$ 132.04	$ 15.55