Condensed Consolidated Statements of Comprehensive Loss (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		138 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012
Condensed Consolidated Statements of Comprehensive Loss [Abstract]
Revenue	$ 728	$ 1,258	$ 2,612	$ 2,517	$ 68,093
Operating expenses:
Research and development	5,010	6,664	10,042	12,926	316,293
General and administrative	2,904	2,735	4,149	5,555	108,025
Restructuring charges					2,037
Acquired in-process research and development					3,916
Total operating expenses	7,914	9,399	14,191	18,481	430,271
Loss from operations	(7,186)	(8,141)	(11,579)	(15,964)	(362,178)
Loss/ (gain) on change in fair value of contingent consideration liability	200	(300)	1,200	(300)	(5,945)
Interest and other income/ (expense), net	409	7	408	17	14,297
Interest expense	(380)	(572)	(813)	(1,174)	(8,682)
Net loss	(6,957)	(9,006)	(10,784)	(17,421)	(362,508)
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	(6,957)	(9,006)	(10,784)	(17,421)	(378,985)
Basic and diluted net loss per share attributable to Alexza common stockholders	$ (0.58)	$ (1.34)	$ (1.03)	$ (2.74)
Shares used to compute basic and diluted net loss per share attributable to Alexza common stockholders	11,903	6,731	10,474	6,360
Change in unrealized gain (loss) on marketable securities		15		15
Comprehensive loss attributed to Alexza common stockholders	$ (6,957)	$ (8,991)	$ (10,784)	$ (17,406)	$ (378,985)