Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended		128 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011
Condensed Consolidated Statements of Operations [Abstract]
Revenue	$ 1,258		$ 2,517		$ 62,338
Operating expenses:
Research and development	6,664	8,290	12,926	15,854	290,915
General and administrative	2,735	3,812	5,555	8,864	97,665
Restructuring charges					2,037
Acquired in-process research and development					3,916
Total operating expenses	9,399	12,102	18,481	24,718	394,533
Loss from operations	(8,141)	(12,102)	(15,964)	(24,718)	(332,195)
Loss on change in fair value of contingent consideration liability	(300)	(449)	(300)	(1,171)	(3,445)
Interest and other income/ (expense), net	7	28	17	9	13,880
Interest expense	(572)	(370)	(1,174)	(425)	(6,854)
Net loss	(9,006)	(12,893)	(17,421)	(26,305)	(328,614)
Consideration paid in excess of noncontrolling interest					(61,566)
Net loss attributed to noncontrolling interest in Symphony Allegro, Inc.					45,089
Net loss attributable to Alexza common stockholders	$ (9,006)	$ (12,893)	$ (17,421)	$ (26,305)	$ (345,091)
Net loss per share attributable to Alexza common stockholders	$ (0.13)	$ (0.24)	$ (0.27)	$ (0.50)
Shares used to compute basic and diluted net loss per share attributable to Alexza common stockholders	67,311	52,798	63,599	52,661