Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended
	Nov. 25, 2015	Nov. 25, 2015	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Jun. 30, 2015
Fair value of total consideration transferred:
Unsecured 12.0% Senior Notes issued to UCB					$ 200,000
Acquisition-related contingent consideration					35,000
Warrant issued to UCB					$ 29,920
Debt instrument, stated percentage	12.00%	12.00%	12.00%		12.00%
Additional tax benefits					$ 100,000
Purchase price allocation of the assets acquired and liabilities assumed
Goodwill			$ 313,451		313,451			$ 141
Revenues			140,114	$ 99,352	373,606	$ 307,561
Net income (loss) attributable to Lannett Company, Inc.			$ (5,490)	$ 36,233	$ 41,211	$ 115,976
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)			$ (0.15)	$ 1.01	$ 1.13	$ 3.25
Diluted (in dollars per share)			$ (0.15)	$ 0.97	$ 1.10	$ 3.13
Acquisition costs incurred by acquirer
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					$ 21,500	$ 21,500
Acquisition costs incurred by acquiree
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					7,400	9,200
KUPI
Acquisitions
Percentage of outstanding equity interest	100.00%	100.00%
Fair value of total consideration transferred:
Cash purchase price paid to KUPI shareholders		$ 1,030,000
Estimated working capital adjustment		(46,202)
Certain amounts reimbursable by UCB		(37,340)
Total cash consideration transferred to KUPI shareholders		946,458
Unsecured 12.0% Senior Notes issued to UCB		200,000
Acquisition-related contingent consideration		35,000
Warrant issued to UCB		29,920
Total consideration to KUPI shareholders		$ 1,211,378
Debt instrument, stated percentage	12.00%	12.00%
Incremental tax cost will be reimbursed (as a percent)	50.00%	50.00%
Business combination recognized identifiable assets acquired and liabilities assumed cash on hand	$ 90,100	$ 90,100
Additional tax benefits	100,000
Purchase price allocation of the assets acquired and liabilities assumed
Cash and cash equivalents			$ 16,877		16,877		$ 16,877
Accounts receivable, net of revenue-related reserves			143,019		143,019		149,209
Inventories			83,600		83,600		83,815
Other current assets			11,405		11,405		12,873
Property, plant and equipment			117,587		117,587		97,418
In-process research and development			129,000		129,000		232,000
Goodwill			313,310		313,310		240,575
Deferred tax assets			4,956		4,956		4,956
Other assets			4,859		4,859		4,859
Total assets acquired			1,276,533		1,276,533		1,274,502
Accounts payable			(19,249)		(19,249)		(19,249)
Accrued expenses			(6,079)		(6,079)		(4,161)
Accrued payroll and payroll-related expenses			(21,040)		(21,040)		(20,731)
Rebates payable			(9,816)		(9,816)		(9,816)
Royalties payable			(3,602)		(3,602)		(3,798)
Other long-term liabilities			(5,369)		(5,369)		(5,369)
Total net assets acquired			1,211,378		1,211,378		1,211,378
Preliminary indemnification assets acquired	15,300	15,300
Compensation related payments	10,400	10,400
Unrecognized tax benefits	$ 4,900	4,900
Revenues			69,933		96,064
Net income (loss) attributable to Lannett Company, Inc.			$ 2,260		(4,047)
Measurement Period Adjustments
Accounts receivable, net of revenue-related reserves					(6,190)
Inventories					(215)
Other current assets					(1,468)
Property, plant and equipment					20,169
In-process research and development					(103,000)
Goodwill					72,735
Total assets acquired					2,031
Accrued expenses					(1,918)
Accrued payroll and payroll-related expenses					(309)
Royalties payable					$ 196
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)			$ 0.06		$ (0.11)
Diluted (in dollars per share)			$ 0.06		$ (0.11)
Acquisition-related expenses					$ 21,500
Unaudited Pro Forma financial results
Revenues			$ 163,712	$ 193,612	520,867	616,083
Net income attributable to Lannett Company, Inc.			$ 896	$ 29,889	$ 55,596	$ 89,527
Earnings per common share attributable to Lannett Company, Inc.:
Basic			$ 0.02	$ 0.83	$ 1.53	$ 2.50
Diluted			$ 0.02	$ 0.80	$ 1.49	$ 2.41
Proforma earnings			$ 896	$ 29,889	$ 55,596	$ 89,527
KUPI | Acquisition-related Costs
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.					(28,900)	(30,700)
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings					(28,900)	(30,700)
KUPI | Acquisition costs incurred by acquiree
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.				(1,000)
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings				$ (1,000)
KUPI | Fair value set-up adjustment
Purchase price allocation of the assets acquired and liabilities assumed
Inventory fair value step-up adjustments		$ 19,100
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.			8,600		14,400	18,900
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings			8,600		14,400	$ 18,900
Senior Notes due 2023
Fair value of total consideration transferred:
Debt instrument, stated percentage	12.00%	12.00%
Senior Notes due 2023 | KUPI
Fair value of total consideration transferred:
Amount of debt issuance for funding the acquisition and transaction expenses		$ 250,000
Senior secured credit facility | KUPI
Fair value of total consideration transferred:
Amount of debt issuance for funding the acquisition and transaction expenses		910,000
Revolving Credit Facility | KUPI
Fair value of total consideration transferred:
Amount of debt issuance for funding the acquisition and transaction expenses		$ 22,800
Product rights | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights			430,000		430,000		409,000
Measurement Period Adjustments
Intangible assets					21,000
Trade name | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights			2,920		2,920		2,920
Other Intangible Assets | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights			$ 19,000		19,000		$ 20,000
Measurement Period Adjustments
Intangible assets					$ (1,000)