Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 39,699	$ 35,943	$ 103,137	$ 112,808
Unrealized (losses) gains on marketable equity securities:
Unrealized holding (losses) gains arising during the period	(29,832)	(2,454)	54,004	13,591
Reclassification adjustment for (gains) losses included in net income	(4,968)	111	(2,503)	517
Unrealized (losses) gains on marketable equity securities, net	(34,800)	(2,343)	51,501	14,108
Unrealized (losses) gains on interest rate swap agreements:
Unrealized interest rate swap (losses) gains arising during the period	(5,474)	1,206	(9,712)	(2,708)
Reclassification adjustment for amortization of interest expense included in net income	727	1,129	1,942	5,742
Unrealized gains on interest rate swap agreements, net	(4,747)	2,335	(7,770)	3,034
Unrealized foreign currency translation losses arising during the period	(9,294)	(12,259)	(17,072)	(9,450)
Reclassification adjustment for (gains) losses included in net income	0	(199)	9,236	(199)
Unrealized foreign currency translation losses arising during the period	(9,294)	(12,458)	(7,836)	(9,649)
Total other comprehensive (loss) income	(48,841)	(12,466)	35,895	7,493
Comprehensive income	(9,142)	23,477	139,032	120,301
Less: comprehensive income attributable to noncontrolling interests	(71)	(1,340)	(954)	(3,842)
Comprehensive (loss) income attributable to Alexandria’s common stockholders	$ (9,213)	$ 22,137	$ 138,078	$ 116,459