Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Stockholders Equity Note [Line Items]
Balance, January 1, 2012		$ 220,141		$ 220,141
Issuance of common stock pursuant to warrant exercises (in shares)		5,805,843				3,757,767	1,220,414
Issuance of common stock pursuant to warrant exercises				87,045
Issuance of common stock pursuant to ARIAD stock plans				8,202
Stock-based compensation				12,289
Payment of tax withholding obligations related to stock based compensation				(2,615)
Net unrealized gains on marketable securities				20
Net loss	(53,213)		13,910	(160,419)	(71,801)
Balance, September 30, 2012	164,663			164,663		220,141
Common stock
Stockholders Equity Note [Line Items]
Balance, January 1, 2012 (in shares)		157,608,702		157,608,702
Balance, January 1, 2012		158		158
Issuance of common stock pursuant to warrant exercises (in shares)				5,805,843
Issuance of common stock pursuant to warrant exercises				6
Issuance of common stock pursuant to ARIAD stock plans (in shares)				3,161,125
Issuance of common stock pursuant to ARIAD stock plans				3
Balance, September 30, 2012 (in shares)	166,575,670			166,575,670
Balance, September 30, 2012	167			167
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Balance, January 1, 2012		776,946		776,946
Issuance of common stock pursuant to warrant exercises				87,039
Issuance of common stock pursuant to ARIAD stock plans				8,199
Stock-based compensation				12,289
Payment of tax withholding obligations related to stock based compensation				(2,615)
Balance, September 30, 2012	881,858			881,858
Accumulated Other Comprehensive Loss
Stockholders Equity Note [Line Items]
Net unrealized gains on marketable securities				20
Balance, September 30, 2012	20			20
Accumulated Deficit
Stockholders Equity Note [Line Items]
Balance, January 1, 2012		(556,963)		(556,963)
Net loss				(160,419)
Balance, September 30, 2012	$ (717,382)			$ (717,382)