Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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				5,681
Stock-based compensation				8,444
Payment of tax withholding obligations related to stock based compensation				(2,615)
Net unrealized losses on marketable securities				(1)
Net loss	(51,312)		(47,762)	(107,206)	(85,711)
Balance, June 30, 2012	211,489			211,489		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				5
Issuance of common stock pursuant to ARIAD stock plans (in shares)				2,657,617
Issuance of common stock pursuant to ARIAD stock plans				3
Balance, June 30, 2012 (in shares)	166,072,162			166,072,162
Balance, June 30, 2012	166			166
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				87,040
Issuance of common stock pursuant to ARIAD stock plans				5,678
Stock-based compensation				8,444
Payment of tax withholding obligations related to stock based compensation				(2,615)
Balance, June 30, 2012	875,493			875,493
Accumulated Other Comprehensive Loss
Stockholders Equity Note [Line Items]
Net unrealized losses on marketable securities				(1)
Balance, June 30, 2012	(1)			(1)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Balance, January 1, 2012		(556,963)		(556,963)
Net loss				(107,206)
Balance, June 30, 2012	$ (664,169)			$ (664,169)