Acquisitions (Details) - USD ($)			3 Months Ended		6 Months Ended
	Nov. 25, 2015	Nov. 25, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2015
Fair value of total consideration transferred:
Unsecured 12.0% Senior Notes issued to UCB					$ 200,000,000
Acquisition-related contingent consideration					35,000,000
Warrant issued to UCB					$ 29,920,000
Debt instrument, stated percentage	12.00%	12.00%	12.00%		12.00%
Additional tax benefits					$ 100,000,000
Purchase price allocation of the assets acquired and liabilities assumed
Goodwill			$ 240,716,000		240,716,000		$ 141,000
Net sales			127,059,000	$ 114,822,000	233,492,000	$ 208,209,000
Net loss attributable to Lannett Company, Inc.			$ 13,520,000	$ 44,811,000	$ 46,701,000	$ 79,743,000
Loss per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)			$ 0.37	$ 1.26	$ 1.28	$ 2.24
Diluted (in dollars per share)			$ 0.36	$ 1.21	$ 1.25	$ 2.15
Acquisition-related expenses			$ 17,585,000	$ 1,999,000	$ 21,527,000	$ 2,069,000
Acquisition costs incurred by acquirer
Loss per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses			17,600,000		21,500,000	21,500,000
Acquisition costs incurred by acquiree
Loss per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses			5,700,000		7,400,000	11,100,000
KUPI
Acquisitions
Percentage of outstanding equity interest	100.00%	100.00%
Fair value of total consideration transferred:
Cash purchase price paid to KUPI shareholders		$ 1,030,000,000
Estimated working capital adjustment		(46,202,000)
Certain amounts reimbursable by UCB		(37,340,000)
Total cash consideration transferred to KUPI shareholders		946,458,000
Unsecured 12.0% Senior Notes issued to UCB		200,000,000
Acquisition-related contingent consideration		35,000,000
Warrant issued to UCB		29,920,000
Total consideration to KUPI shareholders		$ 1,211,378,000
Debt instrument, stated percentage	12.00%	12.00%
Incremental tax cost will be reimbursed (as a percent)	50.00%	50.00%
Business Combination Recognized IdentifiableAssets Acquired And Liabilities AssumedCash on hand	$ 90,100,000	$ 90,100,000
Additional tax benefits	100,000,000
Purchase price allocation of the assets acquired and liabilities assumed
Cash and cash equivalents	16,877,000	16,877,000
Accounts receivable, net of revenue-related reserves	149,209,000	149,209,000
Inventories	83,815,000	83,815,000
Other current assets	12,873,000	12,873,000
Property, plant and equipment	97,418,000	97,418,000
In-process research and development	232,000,000	232,000,000
Goodwill	240,575,000	240,575,000
Deferred tax assets	4,956,000	4,956,000
Other assets	4,859,000	4,859,000
Total assets acquired	1,274,502,000	1,274,502,000
Accounts payable	(19,249,000)	(19,249,000)
Accrued expenses	(4,161,000)	(4,161,000)
Accrued payroll and payroll-related expenses	(20,731,000)	(20,731,000)
Rebates payable	(9,816,000)	(9,816,000)
Royalties payable	(3,798,000)	(3,798,000)
Other long-term liabilities	(5,369,000)	(5,369,000)
Total net assets acquired	1,211,378,000	1,211,378,000
Preliminary indemnification assets acquired	15,000,000	15,000,000
Compensation related payments	10,100,000	10,100,000
Unrecognized tax benefits	$ 4,900,000	4,900,000
Net sales					26,131,000
Net loss attributable to Lannett Company, Inc.					$ (6,307,000)
Loss per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)					$ (0.17)
Diluted (in dollars per share)					$ (0.17)
Acquisition-related expenses			17,600,000		$ 21,500,000
Unaudited Pro Forma financial results
Revenues			173,189,000	224,982,000	357,155,000	422,471,000
Net income attributable to Lannett Company, Inc.			$ 28,810,000	$ 56,636,000	$ 55,129,000	$ 60,119,000
Earnings per common share attributable to Lannett Company, Inc.:
Basic			$ 0.79	$ 1.59	$ 1.52	$ 1.69
Diluted			$ 0.77	$ 1.53	$ 1.47	$ 1.62
Proforma earnings			$ 28,810,000	$ 56,636,000	$ 55,129,000	$ 60,119,000
KUPI | Acquisition-related Costs
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.			(23,300,000)		(28,900,000)	(32,600,000)
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings			(23,300,000)		(28,900,000)	(32,600,000)
KUPI | Acquisition costs incurred by acquiree
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.				(2,900,000)
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings				$ (2,900,000)
KUPI | Fair value set-up adjustment
Purchase price allocation of the assets acquired and liabilities assumed
Inventory fair value step-up adjustments		$ 19,100,000
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.			5,800,000		5,800,000	19,100,000
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings			$ 5,800,000		$ 5,800,000	$ 19,100,000
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		$ 250,000,000
Senior secured credit facility | KUPI
Fair value of total consideration transferred:
Amount of debt issuance for funding the acquisition and transaction expenses		910,000,000
Revolving Credit Facility | KUPI
Fair value of total consideration transferred:
Amount of debt issuance for funding the acquisition and transaction expenses		22,800,000
Product rights | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights	$ 409,000,000	409,000,000
Trade name | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights	2,920,000	2,920,000
Other Intangible Assets | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights	$ 20,000,000	$ 20,000,000