Consolidated Statement Of Stockholders' Equity (USD $)	3 Months Ended	6 Months Ended	12 Months Ended									107 Months Ended
	Mar. 31, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2008	Sep. 30, 2007	Sep. 30, 2006	Sep. 30, 2005	Sep. 30, 2004	Sep. 30, 2003	Mar. 31, 2012
Stock issued during period, value, new issues		$ 525,000	$ 43,279	$ 1,066,051					$ 50,000	$ (150,469)
Reclassification of former Unidym mezzanine debt to equity					2,000,000
Stock issuance cost charged to additional paid-in capital										(991,318)
Net loss attributable to Arrowhead	(5,584,115)	(8,270,913)	(3,492,399)	(6,957,038)	(19,308,392)	(27,241,639)	(30,712,947)	(19,961,961)	(6,733,427)	(751,255)	(95,238)	(139,813,195)
Stock issued during period, value, stock options exercised		23,833	13,884	7,631		290,027	434,727	341,537		15,000
Adjustments to additional paid in capital, share-based compensation, requisite service period recognition, value		421,268	1,404,640	1,582,149	2,676,170	3,187,397	2,175,544	1,369,478	508,513	175,653
Adjustments to additional paid in capital, reallocation of noncontrolling interest				300,000	16,297	1,720,962			230,087
Issuance of preferred stock in subsidiary			1,618,509	300,000
Divestiture of Unidym			254,275
Net loss attributable to Arrowhead	(5,335,233)	(7,820,737)										(121,528,529)
Balance	11,566,686	11,566,686	12,564,168	8,078,296	4,857,936	12,302,609	26,456,577	31,605,644	28,026,657	11,227,149	1,419,762	11,566,686
Common Stock [Member] | Issued For Cash At $0.01 Per Unit [Member]
Stock issued during period, value, new issues											3,000
Stock issued during period, shares, new issues											300,000
Common Stock [Member] | Issued For Cash At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										475	1,680
Stock issued during period, shares, new issues										47,500	168,000
Common Stock [Member] | Issued For Marketable Securities At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										500
Stock issued during period, shares, new issues										50,000
Common Stock [Member] | Issued For Cash At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										6,609
Stock issued during period, shares, new issues										660,879
Common Stock [Member] | Issued as a Gift for $10.90 Per Share [Member]
Stock issued during period, value, new issues										163
Stock issued during period, shares, new issues										15,000
Common Stock [Member] | Issued As Stock Issuance Cost At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										356
Stock issued during period, shares, new issues										35,623
Common Stock [Member] | Exercised At $2.00 Per Share [Member]
Stock issued during period, value, stock options exercised										75
Stock issued during period, shares, stock options exercised										7,500
Common Stock [Member] | Exercised At $10.00 Per Share [Member]
Stock issued during period, value, new issues									25
Stock issued during period, shares, new issues									2,500
Stock issued during period, value, stock options exercised										6
Stock issued during period, shares, stock options exercised										600
Common Stock [Member] | Exercised At $15.00 Per Share [Member]
Stock issued during period, value, new issues									13,813
Stock issued during period, shares, new issues									1,381,289
Common Stock [Member] | Issued To Purchase Insert Therapeutics Share At $39.80 Per Share [Member]
Stock issued during period, value, new issues									502
Stock issued during period, shares, new issues									50,226
Common Stock [Member] | Issued At $48.80 Per Share [Member]
Stock issued during period, value, new issues								205
Stock issued during period, shares, new issues								20,485
Common Stock [Member] | Issued At $38.40 Per Share [Member]
Stock issued during period, value, new issues								15
Stock issued during period, shares, new issues								1,500
Common Stock [Member] | Issued At $35.00 Per Share [Member]
Stock issued during period, value, new issues								5,590
Stock issued during period, shares, new issues								559,000
Common Stock [Member] | Issued At $59.10 Per Share [Member]
Stock issued during period, value, new issues								25
Stock issued during period, shares, new issues								2,536
Common Stock [Member] | Issued To Purchase Calando Pharmaceuticals Inc At $51.70 Per Share [Member]
Stock issued during period, value, new issues								208
Stock issued during period, shares, new issues								20,838
Common Stock [Member] | Issued At $57.80 Per Share [Member]
Stock issued during period, value, new issues							2,849
Stock issued during period, shares, new issues							284,945
Common Stock [Member] | Issued For Purchase Of Carbon Nanotechnologies Inc At $37.70 Per Share [Member]
Stock issued during period, value, new issues							1,431
Stock issued during period, shares, new issues							143,122
Common Stock [Member] | Issued At Approximately $18.00 Per Share Net [Member]
Stock issued during period, value, new issues						3,867
Stock issued during period, shares, new issues						386,399
Common Stock [Member] | Issued At $27.20 Per Share To Rice University [Member]
Stock issued during period, value, new issues						50
Stock issued during period, shares, new issues						5,000
Common Stock [Member] | Issued At $28.30 Per Share To Purchase Shares Of Unidym Inc [Member]
Stock issued during period, value, new issues						71
Stock issued during period, shares, new issues						7,055
Common Stock [Member] | Issued At $29.50 per Share To Purchase MASA Energy LLC [Member]
Stock issued during period, value, new issues						105
Stock issued during period, shares, new issues						10,505
Common Stock [Member] | Issued At $21.90 Per Share To Unidym For The Acquisition Of Nanoconduction [Member]
Stock issued during period, value, new issues						114
Stock issued during period, shares, new issues						11,416
Common Stock [Member] | Issued At $21.80 Per Share [Member]
Stock issued during period, value, new issues						15
Stock issued during period, shares, new issues						1,500
Common Stock [Member] | Issued At $5.50 Per Share To Unidym Stockholder In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					2,059
Stock issued during period, shares, new issues					205,839
Common Stock [Member] | Issued At $5.20 Per Share To TEL Ventures In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					2,222
Stock issued during period, shares, new issues					222,222
Common Stock [Member] | Issued At $3.00 Per Share [Member]
Stock issued during period, value, new issues					9,197
Stock issued during period, shares, new issues					919,664
Common Stock [Member] | Issued At $6.30 Per Share [Member]
Stock issued during period, value, new issues				5,083
Stock issued during period, shares, new issues				508,343
Common Stock [Member] | Issued At $13.12 Per Share [Member]
Stock issued during period, value, new issues				6,593
Stock issued during period, shares, new issues				659,299
Common Stock [Member] | Issued At $3.80 Per Share [Member]
Stock issued during period, value, new issues			14,574
Stock issued during period, shares, new issues			1,458,917
Common Stock [Member] | Issued At $3.70 Per Share [Member]
Stock issued during period, value, new issues		6,750
Stock issued during period, shares, new issues		675,000
Common Stock [Member] | Issued at $4.00 Per Share [Member]
Stock issued during period, value, new issues		1,000
Stock issued during period, shares, new issues		100,000
Common Stock [Member] | Issued To Unidym Stockholders In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues				153
Stock issued during period, shares, new issues				15,318
Common Stock [Member] | Issued To Calando Stockholders In Exchange For Calando's Shares [Member]
Stock issued during period, value, new issues				1,220
Stock issued during period, shares, new issues				122,000
Common Stock [Member] | Issued In Acquisition [Member]
Stock issued during period, value, new issues		9,017
Stock issued during period, shares, new issues		901,702
Common Stock [Member] | Issued Under Committed Capital Agreement [Member]
Stock issued during period, value, new issues		689
Stock issued during period, shares, new issues		68,926
Common Stock [Member]
Stock issued during period, value, new issues		1,382	87	2,251					12	706
Stock issued during period, shares, new issues		138,158	8,656	225,189					1,250	70,553
Stock issued during period, value, stock options exercised		45	27	7		106	186	116		75
Stock issued during period, shares, stock options exercised		4,583	2,700	688		10,536	18,616	11,579		7,500
Fractional shares redeemed in reverse stock split		(131)
Preferred stock converted to common stock		276
Preferred stock converted to common stock, shares		275,782
Balance	105,582	105,582	86,423	71,735	56,428	42,950	38,622	34,156	27,997	13,645	4,680	105,582
Balance, shares	10,806,306	10,806,306	8,642,286	7,172,014	5,641,177	4,293,452	3,861,042	3,414,359	2,798,419	1,363,155	468,000	10,806,306
Preferred Stock [Member] | Preferred Stock Issued At $1,000 Per Share [Member]
Stock issued during period, value, new issues		1
Stock issued during period, shares, new issues		1,015
Preferred Stock [Member]
Preferred stock converted to common stock		(1)
Preferred stock converted to common stock, shares		(1,015)
Additional Paid-In Capital [Member] | Issued For Cash At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										474,525	1,678,320
Additional Paid-In Capital [Member] | Issued For Marketable Securities At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										499,500
Additional Paid-In Capital [Member] | Issued For Cash At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										9,906,573
Additional Paid-In Capital [Member] | Stock Issuance Cost Charged To Additional Paid In Capital [Member]
Stock issuance cost charged to additional paid-in capital										(96,500)	(168,000)
Additional Paid-In Capital [Member] | Arrowheads Increase In Proportionate Share Of Insert Therapeutics Equity [Member]
Adjustments to additional paid in capital, reallocation of noncontrolling interest							2,401,394
Additional Paid-In Capital [Member] | Arrowheads Increase In Proportionate Share Of Calando's Equity [Member]
Adjustments to additional paid in capital, reallocation of noncontrolling interest					2,120,250
Additional Paid-In Capital [Member] | Issued as a Gift for $10.90 Per Share [Member]
Stock issued during period, value, new issues										162,587
Additional Paid-In Capital [Member] | Issued As Stock Issuance Cost At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										533,988
Additional Paid-In Capital [Member] | Exercised At $2.00 Per Share [Member]
Stock issued during period, value, stock options exercised										14,925
Additional Paid-In Capital [Member] | Exercised At $10.00 Per Share [Member]
Stock issued during period, value, new issues									24,975
Stock issued during period, value, stock options exercised										5,994
Additional Paid-In Capital [Member] | Exercised At $15.00 Per Share [Member]
Stock issued during period, value, new issues									20,705,522
Additional Paid-In Capital [Member] | Issued To Purchase Insert Therapeutics Share At $39.80 Per Share [Member]
Stock issued during period, value, new issues									1,999,498
Additional Paid-In Capital [Member] | Issued At $48.80 Per Share [Member]
Stock issued during period, value, new issues								999,795
Additional Paid-In Capital [Member] | Issued At $38.40 Per Share [Member]
Stock issued during period, value, new issues								57,585
Additional Paid-In Capital [Member] | Issued At $35.00 Per Share [Member]
Stock issued during period, value, new issues								19,539,410
Additional Paid-In Capital [Member] | Issued At $59.10 Per Share [Member]
Stock issued during period, value, new issues								149,975
Additional Paid-In Capital [Member] | Issued To Purchase Calando Pharmaceuticals Inc At $51.70 Per Share [Member]
Stock issued during period, value, new issues								1,077,125
Additional Paid-In Capital [Member] | Issued At $57.80 Per Share [Member]
Stock issued during period, value, new issues							15,149,366
Additional Paid-In Capital [Member] | Issued For Purchase Of Carbon Nanotechnologies Inc At $37.70 Per Share [Member]
Stock issued during period, value, new issues							5,398,569
Additional Paid-In Capital [Member] | Issued At Approximately $18.00 Per Share Net [Member]
Stock issued during period, value, new issues						6,956,718
Additional Paid-In Capital [Member] | Issued At $27.20 Per Share To Rice University [Member]
Stock issued during period, value, new issues						135,950
Additional Paid-In Capital [Member] | Issued At $28.30 Per Share To Purchase Shares Of Unidym Inc [Member]
Stock issued during period, value, new issues						199,929
Additional Paid-In Capital [Member] | Issued At $29.50 per Share To Purchase MASA Energy LLC [Member]
Stock issued during period, value, new issues						309,895
Additional Paid-In Capital [Member] | Issued At $21.90 Per Share To Unidym For The Acquisition Of Nanoconduction [Member]
Stock issued during period, value, new issues						249,886
Additional Paid-In Capital [Member] | Issued At $21.80 Per Share [Member]
Stock issued during period, value, new issues						32,685
Additional Paid-In Capital [Member] | Issued At $5.50 Per Share To Unidym Stockholder In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					1,131,617
Additional Paid-In Capital [Member] | Issued At $5.20 Per Share To TEL Ventures In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					1,156,111
Additional Paid-In Capital [Member] | Issued At $3.00 Per Share [Member]
Stock issued during period, value, new issues					2,749,796
Additional Paid-In Capital [Member] | Issued At $6.30 Per Share [Member]
Stock issued during period, value, new issues				3,217,813
Additional Paid-In Capital [Member] | Issued At $13.12 Per Share [Member]
Stock issued during period, value, new issues				3,692,078
Additional Paid-In Capital [Member] | Issued At $3.80 Per Share [Member]
Stock issued during period, value, new issues			4,629,110
Additional Paid-In Capital [Member] | Issued At $3.70 Per Share [Member]
Stock issued during period, value, new issues		2,490,750
Additional Paid-In Capital [Member] | Issued at $4.00 Per Share [Member]
Stock issued during period, value, new issues		399,000
Additional Paid-In Capital [Member] | Issuance Of Common Stock For Subscription [Member]
Stock issued during period, value, new issues			900,000
Additional Paid-In Capital [Member] | Series D Preferred Stock Issued For Subscription In Unidym [Member]
Issuance of preferred stock in subsidiary					300,000
Additional Paid-In Capital [Member] | Issued To Unidym Stockholders In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues				(1,435)
Additional Paid-In Capital [Member] | Issued To Calando Stockholders In Exchange For Calando's Shares [Member]
Stock issued during period, value, new issues				(160,667)
Additional Paid-In Capital [Member] | Issued In Acquisition [Member]
Stock issued during period, value, new issues		4,138,813
Additional Paid-In Capital [Member] | Issued Under Committed Capital Agreement [Member]
Stock issued during period, value, new issues		(689)
Additional Paid-In Capital [Member] | Preferred Stock Issued At $1,000 Per Share [Member]
Stock issued during period, value, new issues		1,014,999
Additional Paid-In Capital [Member]
Stock issued during period, value, new issues		523,618	43,192	1,063,600					49,988	(151,175)
Reclassification of former Unidym mezzanine debt to equity					2,000,000
Stock issuance cost charged to additional paid-in capital										(991,318)
Stock issued during period, value, stock options exercised		23,788	13,857	7,624		289,921	434,541	341,421		14,925
Adjustments to additional paid in capital, share-based compensation, requisite service period recognition, value		421,268	1,404,640	1,582,149	2,676,170	3,187,397	2,175,544	1,369,478	508,513	175,653
Adjustments to additional paid in capital, reallocation of noncontrolling interest			(849,707)	245,345	16,297	1,720,962			230,087
Issuance of preferred stock in subsidiary			1,618,509
Amortization of discount on Unidym Series D Preferred Stock					163,960
Preferred stock converted to common stock		(275)
Balance	136,487,707	136,487,707	127,476,435	119,716,834	110,070,327	97,756,126	84,672,783	59,113,369	35,578,580	12,059,997	1,510,320	136,487,707
Subscription Receivable [Member] | Issued At $3.70 Per Share [Member]
Stock issued during period, value, new issues		(2,497,500)
Subscription Receivable [Member] | Issuance Of Common Stock For Subscription [Member]
Stock issued during period, value, new issues		1,232,500	(900,000)
Subscription Receivable [Member] | Series D Preferred Stock Issued For Subscription In Unidym [Member]
Issuance of preferred stock in subsidiary					(300,000)
Subscription Receivable [Member] | Preferred Stock Issued At $1,000 Per Share [Member]
Stock issued during period, value, new issues		(500,000)
Subscription Receivable [Member]
Issuance of preferred stock in subsidiary				300,000
Balance	(2,665,000)	(2,665,000)	(900,000)		(300,000)							(2,665,000)
Accumulated Deficit During The Development Stage [Member]
Net loss attributable to Arrowhead		(7,820,737)	(3,128,885)	(5,774,048)	(19,308,392)	(27,089,030)	(29,931,118)	(18,997,209)	(6,854,918)	(2,528,954)	(95,238)
Amortization of discount on Unidym Series D Preferred Stock					(163,960)
Balance	(121,692,489)	(121,692,489)	(113,871,752)	(110,742,867)	(104,968,819)	(85,496,467)	(58,407,437)	(28,476,319)	(9,479,110)	(2,624,192)	(95,238)	(121,692,489)
Noncontrolling Interest [Member] | Issued To Unidym Stockholders In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues				1,282
Noncontrolling Interest [Member] | Issued To Calando Stockholders In Exchange For Calando's Shares [Member]
Stock issued during period, value, new issues				159,447
Stock issued during period, value, stock options exercised		8,000
Noncontrolling Interest [Member]
Stock issued during period, value, new issues				200
Net loss attributable to Arrowhead		(450,176)	(363,514)	(1,182,990)		(152,609)	(781,829)	(964,752)	121,491	1,777,699
Adjustments to additional paid in capital, reallocation of noncontrolling interest			849,707	54,655
Divestiture of Unidym			254,275
Balance	(669,114)	(669,114)	(226,938)	(967,406)			152,609	934,438	1,899,190	1,777,699		(669,114)
Issued For Cash At $0.01 Per Unit [Member]
Stock issued during period, value, new issues											3,000
Issued For Cash At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										475,000	1,680,000
Issued For Marketable Securities At $10.00 Per Unit [Member]
Stock issued during period, value, new issues										500,000
Issued For Cash At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										9,913,182
Stock Issuance Cost Charged To Additional Paid In Capital [Member]
Stock issuance cost charged to additional paid-in capital										(96,500)	(168,000)
Arrowheads Increase In Proportionate Share Of Insert Therapeutics Equity [Member]
Adjustments to additional paid in capital, reallocation of noncontrolling interest							2,401,394
Arrowheads Increase In Proportionate Share Of Calando's Equity [Member]
Adjustments to additional paid in capital, reallocation of noncontrolling interest					2,120,250
Issued as a Gift for $10.90 Per Share [Member]
Stock issued during period, value, new issues										162,750
Issued As Stock Issuance Cost At $15.00 Per Unit [Member]
Stock issued during period, value, new issues										534,344
Exercised At $2.00 Per Share [Member]
Stock issued during period, value, stock options exercised										15,000
Exercised At $10.00 Per Share [Member]
Stock issued during period, value, new issues									25,000
Stock issued during period, value, stock options exercised										6,000
Exercised At $15.00 Per Share [Member]
Stock issued during period, value, new issues									20,719,335
Issued To Purchase Insert Therapeutics Share At $39.80 Per Share [Member]
Stock issued during period, value, new issues									2,000,000
Issued At $48.80 Per Share [Member]
Stock issued during period, value, new issues								1,000,000
Issued At $38.40 Per Share [Member]
Stock issued during period, value, new issues								57,600
Issued At $35.00 Per Share [Member]
Stock issued during period, value, new issues								19,545,000
Issued At $59.10 Per Share [Member]
Stock issued during period, value, new issues								150,000
Issued To Purchase Calando Pharmaceuticals Inc At $51.70 Per Share [Member]
Stock issued during period, value, new issues								1,077,333
Issued At $57.80 Per Share [Member]
Stock issued during period, value, new issues							15,152,215
Issued For Purchase Of Carbon Nanotechnologies Inc At $37.70 Per Share [Member]
Stock issued during period, value, new issues							5,400,000
Issued At Approximately $18.00 Per Share Net [Member]
Stock issued during period, value, new issues						6,960,585
Issued At $27.20 Per Share To Rice University [Member]
Stock issued during period, value, new issues						136,000
Issued At $28.30 Per Share To Purchase Shares Of Unidym Inc [Member]
Stock issued during period, value, new issues						200,000
Issued At $29.50 per Share To Purchase MASA Energy LLC [Member]
Stock issued during period, value, new issues						310,000
Issued At $21.90 Per Share To Unidym For The Acquisition Of Nanoconduction [Member]
Stock issued during period, value, new issues						250,000
Issued At $21.80 Per Share [Member]
Stock issued during period, value, new issues						32,700
Issued At $5.50 Per Share To Unidym Stockholder In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					1,133,676
Issued At $5.20 Per Share To TEL Ventures In Exchange For Unidym's Shares [Member]
Stock issued during period, value, new issues					1,158,333
Issued At $3.00 Per Share [Member]
Stock issued during period, value, new issues					2,758,993
Issued At $6.30 Per Share [Member]
Stock issued during period, value, new issues				3,222,896
Issued At $13.12 Per Share [Member]
Stock issued during period, value, new issues				3,698,671
Issued At $3.80 Per Share [Member]
Stock issued during period, value, new issues			4,643,684
Issued at $4.00 Per Share [Member]
Stock issued during period, value, new issues		400,000
Issuance Of Common Stock For Subscription [Member]
Stock issued during period, value, new issues		1,232,500
Issued To Calando Stockholders In Exchange For Calando's Shares [Member]
Stock issued during period, value, stock options exercised		8,000
Issued In Acquisition [Member]
Stock issued during period, value, new issues		4,147,830
Preferred Stock Issued At $1,000 Per Share [Member]
Stock issued during period, value, new issues		$ 515,000