Acquisitions (Details) - USD ($)		3 Months Ended												12 Months Ended
	Nov. 25, 2015	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014
Fair value of total consideration transferred:
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%
Additional tax benefits														$ 100,000,000
Purchase price allocation of the assets acquired and liabilities assumed
Goodwill		$ 333,611,000				$ 141,000								333,611,000	$ 141,000
Total net sales		168,887,000	$ 140,114,000	$ 127,059,000	$ 106,433,000	99,276,000	$ 99,352,000	$ 114,822,000	$ 93,387,000	$ 80,619,000	$ 79,997,000	$ 67,326,000	$ 45,829,000	542,493,000	406,837,000	$ 273,771,000
Loss attributable to Lannett Company, Inc.		$ 3,571,000	$ (5,490,000)	$ 13,520,000	$ 33,181,000	$ 33,943,000	$ 36,233,000	$ 44,811,000	$ 34,932,000	$ 23,535,000	$ 22,995,000	$ 16,566,000	$ (5,995,000)	$ 44,782,000	$ 149,919,000	$ 57,101,000
Loss per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)		$ 0.10	$ (0.15)	$ 0.37	$ 0.91	$ 0.94	$ 1.01	$ 1.26	$ 0.98	$ 0.66	$ 0.66	$ 0.48	$ (0.20)	$ 1.23	$ 4.18	$ 1.70
Diluted (in dollars per share)		$ 0.10	$ (0.15)	$ 0.36	$ 0.89	$ 0.91	$ 0.97	$ 1.21	$ 0.94	$ 0.64	$ 0.63	$ 0.46	$ (0.20)	$ 1.20	$ 4.04	$ 1.62
KUPI
Acquisitions
Percentage of outstanding equity interest	100.00%
Fair value of total consideration transferred:
Cash purchase price paid to KUPI shareholders	$ 1,030,000,000
Working capital adjustment	(41,605,000)
Certain amounts reimbursed by UCB	(37,340,000)
Total cash consideration transferred to KUPI shareholders	951,055,000
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	$ 1,215,975,000
Incremental tax cost will be reimbursed (as a percent)	50.00%
Business combination recognized identifiable assets acquired and liabilities assumed cash on hand	$ 94,600,000
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												16,877,000
Accounts receivable, net of revenue-related reserves	149,209,000	135,363,000												135,363,000
Inventories	83,815,000	84,009,000												84,009,000
Other current assets	12,873,000	11,238,000												11,238,000
Property, plant and equipment	97,418,000	111,849,000												111,849,000
In-process research and development	232,000,000	125,000,000												125,000,000
Goodwill	240,575,000	333,470,000												333,470,000
Deferred tax assets	4,956,000	4,186,000												4,186,000
Other assets	4,859,000	10,218,000												10,218,000
Total assets acquired	1,274,502,000	1,281,130,000												1,281,130,000
Accounts payable	(19,249,000)	(19,249,000)												(19,249,000)
Accrued expenses	(4,161,000)	(6,079,000)												(6,079,000)
Accrued payroll and payroll-related expenses	(20,731,000)	(21,040,000)												(21,040,000)
Rebates payable	(9,816,000)	(9,816,000)												(9,816,000)
Royalties payable	(3,798,000)	(3,602,000)												(3,602,000)
Other liabilities	(5,369,000)	(5,369,000)												(5,369,000)
Total net assets acquired	1,211,378,000	$ 1,215,975,000												1,215,975,000
Preliminary indemnification assets acquired	20,700,000
Compensation related payments	10,400,000
Unrecognized tax benefits	4,900,000
Chargeback and rebate-related items	5,400,000
Inventory fair value step-up adjustments	$ 19,100,000
Total net sales														165,649,000
Loss attributable to Lannett Company, Inc.														(3,431,000)
Measurement Period Adjustments
Accounts receivable, net of revenue-related reserves														(13,846,000)
Inventories														194,000
Other current assets														(1,635,000)
Property, plant and equipment														14,431,000
In-process research and development														(107,000,000)
Goodwill														92,895,000
Deferred tax assets														(770,000)
Other assets														5,359,000
Total assets acquired														6,628,000
Accrued expenses														(1,918,000)
Accrued payroll and payroll-related expenses														(309,000)
Royalties payable														196,000
Total net assets acquired														4,597,000
Working capital adjustments														$ 4,600,000
Loss per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)														$ (0.09)
Diluted (in dollars per share)														$ (0.09)
Unaudited Pro Forma financial results
Total net Sales														$ 689,754,000	$ 809,379,000
Net income attributable to Lannett Company, Inc.														$ 61,916,000	$ 116,119,000
Earnings per common share attributable to Lannett Company, Inc.:
Basic														$ 1.70	$ 3.24
Diluted														$ 1.66	$ 3.13
Proforma earnings														$ 61,916,000	$ 116,119,000
KUPI | Acquisition-related Costs
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.														28,900,000	28,900,000
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings														28,900,000	28,900,000
KUPI | Acquisition costs incurred by acquirer
Loss per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses														21,500,000	21,500,000
KUPI | Acquisition costs incurred by acquiree
Loss per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses														7,400,000	7,400,000
KUPI | Fair value set-up adjustment
Unaudited Pro Forma financial results
Net income attributable to Lannett Company, Inc.														17,000,000	18,900,000
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings														$ 17,000,000	$ 18,900,000
Senior Notes due 2023
Fair value of total consideration transferred:
Debt instrument, stated percentage	12.00%
Senior Notes due 2023 | KUPI
Fair value of total consideration transferred:
Debt instrument, stated percentage		12.00%												12.00%
Amount of debt issuance for funding the acquisition and transaction expenses	$ 250,000,000
Term loans | 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
In-process Research and Development
Purchase price allocation of the assets acquired and liabilities assumed
Impairment charge related to intangible assets		$ 8,000,000
In-process Research and Development | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Impairment charge related to intangible assets		8,000,000
Product rights | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights	409,000,000	427,000,000												$ 427,000,000
Measurement Period Adjustments
Intangible assets														18,000,000
Trade name | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Product Rights	2,920,000	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	$ 19,000,000												19,000,000
Measurement Period Adjustments
Intangible assets														$ (1,000,000)