Changes in Stockholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Stockholders Equity Note [Line Items]
Balance, January 1, 2012	$ 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	3,377
Stock-based compensation	4,913
Payment of tax withholding obligations related to stock-based compensation	(2,302)
Net unrealized losses on marketable securities	(15)
Net loss	(55,894)	(37,949)
Balance, March 31, 2012	257,265		220,141
Common Stock
Stockholders Equity Note [Line Items]
Balance, January 1, 2012 (in shares)	157,608,702
Balance, January 1, 2012	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)	2,059,563
Issuance of common stock pursuant to ARIAD stock plans	2
Balance, March 31, 2012 (in shares)	165,474,108
Balance, March 31, 2012	165
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Balance, January 1, 2012	776,946
Issuance of common stock pursuant to warrant exercises	87,040
Issuance of common stock pursuant to ARIAD stock plans	3,375
Stock-based compensation	4,913
Payment of tax withholding obligations related to stock-based compensation	(2,302)
Balance, March 31, 2012	869,972
Accumulated Other Comprehensive Loss
Stockholders Equity Note [Line Items]
Net unrealized losses on marketable securities	(15)
Balance, March 31, 2012	(15)
Accumulated Deficit
Stockholders Equity Note [Line Items]
Balance, January 1, 2012	(556,963)
Net loss	(55,894)
Balance, March 31, 2012	$ (612,857)