Significant Transactions - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended			1 Months Ended				12 Months Ended			9 Months Ended			3 Months Ended		9 Months Ended			9 Months Ended
	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Steering Committee Services	Sep. 30, 2012 Second Amendment	Sep. 30, 2012 Sigma Tau	Sep. 30, 2011 Sigma Tau	Sep. 30, 2012 Sigma Tau	Sep. 30, 2011 Sigma Tau	Dec. 31, 2011 Sigma Tau	Jun. 30, 2010 Sigma Tau Original Agreement	Jun. 30, 2010 Sigma Tau Original Agreement Up-front Payment Arrangement	Sep. 30, 2012 Sigma Tau First Amendment	Sep. 30, 2012 Sigma Tau First Amendment Up-front Payment Arrangement	Dec. 31, 2011 Sigma Tau Second Amendment Up-front Payment Arrangement	Dec. 31, 2011 Sigma Tau Second Amendment Additional Up-front Payment Arrangement	Dec. 31, 2011 Sigma Tau Third Amendment	Sep. 30, 2012 Sigma Tau Fourth Amendment	Sep. 30, 2012 Sigma Tau Fourth Amendment Maximum	Sep. 30, 2012 Sigma Tau Fourth Amendment Minimum	Sep. 30, 2012 CMIC Co., Ltd, (CMIC)	Sep. 30, 2011 CMIC Co., Ltd, (CMIC)	Sep. 30, 2012 CMIC Co., Ltd, (CMIC)	Sep. 30, 2011 CMIC Co., Ltd, (CMIC)	Dec. 31, 2011 CMIC Co., Ltd, (CMIC)	Sep. 30, 2012 CMIC Co., Ltd, (CMIC) Maximum	Sep. 30, 2012 CMIC Co., Ltd, (CMIC) Minimum	Sep. 30, 2012 CMIC Co., Ltd, (CMIC) Up-front Payment Arrangement
Significant Transactions [Line Items]
Description of collaborative agreement	In June 2010, the Company entered into a strategic collaboration agreement with Sigma-Tau Rare Diseases S.A. (as successor-in-interest to Defiante Farmaceutica S.A.) (Sigma-Tau) to develop and commercialize subcutaneous ecallantide for the treatment of HAE and other therapeutic indications throughout Europe, North Africa, the Middle East and Russia. In December 2010, the original agreement was amended to expand the partnership to commercialize KALBITOR for the treatment of HAE in Australia and New Zealand (the first amendment). In May 2011, the Company further amended its agreement with Sigma-Tau to include development and commercialization rights in Latin America (excluding Mexico), the Caribbean and certain Asian territories (the second amendment). Three subsequent amendments to this agreement eliminated rights that Dyax had previously granted to Sigma-Tau for the Asian territories, the Middle East, North Africa, Latin America and the Caribbean
Collaboration arrangement payment														$ 2,500,000		$ 500,000	$ 4,000,000	$ 3,000,000												$ 4,000,000
Common stock purchase													636,132		151,515
Common stock share price per share													$ 3.93		$ 3.30
Premium on common stock purchase													50.00%		50.00%
Aggregate purchase Price													2,500,000		500,000
Eliminated payment obligation of certain Asian territories																			3,000,000
Description of right and obligation of collaborative agreement																				Under the terms of the fourth and fifth amendments, Sigma-Tau's rights to the Middle East, Latin America and the Caribbean were eliminated. The Company agreed to make payments to Sigma-Tau ranging from 5%-12.5% of the amounts received by the Company as a result of any future product sales for certain countries in these territories.
Percentage of contribution payment from product sale																					12.50%	5.00%
Proceed from development and sales milestones				100,000,000																								102,000,000
Percentage of revenue to receive from development and sales milestones				41.00%																								24.00%	20.00%
Revenue		13,101,000	10,132,000	38,620,000	40,221,000	190,000	4,800,000	69,000.0	280,000.0	156,000.0	12,200,000												189,000	148,000	566,000	444,000
Deferred revenue							$ 2,400,000	$ 111,000		$ 111,000		$ 158,000											$ 2,700,000		$ 2,700,000		$ 3,300,000