Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		11 Months Ended
	Nov. 25, 2015	Nov. 25, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Jun. 30, 2016
Fair value of total consideration transferred:
Acquisition-related contingent consideration			$ 35,000
Additional tax benefits			100,000
Purchase price allocation of the assets acquired and liabilities assumed
Goodwill			339,566		$ 339,566	$ 333,611
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
Working capital adjustment		(41,605)
Certain amounts reimbursed by UCB		(37,340)
Total cash consideration transferred to KUPI shareholders		951,055
12% Senior Notes Issued to UCB		200,000
Acquisition-related contingent consideration		35,000
Warrant issued to UCB		29,920
Total consideration to KUPI shareholders		$ 1,215,975
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	$ 94,600	$ 94,600
Additional tax benefits	100,000
Purchase price allocation of the assets acquired and liabilities assumed
Cash and cash equivalents			16,877		16,877
Accounts receivable, net of revenue-related reserves			129,408		129,408
Inventories			84,009		84,009
Other current assets			11,238		11,238
Property, plant and equipment			111,849		111,849
In-process research and development			125,000		125,000
Goodwill			339,425		339,425
Deferred tax assets			4,186		4,186
Other assets			10,218		10,218
Total assets acquired			1,281,130		1,281,130
Accounts payable			(19,249)		(19,249)
Accrued expenses			(6,079)		(6,079)
Accrued payroll and payroll-related expenses			(21,040)		(21,040)
Rebates payable			(9,816)		(9,816)
Royalties payable			(3,602)		(3,602)
Other liabilities			(5,369)		(5,369)
Total net assets acquired			1,215,975		1,215,975
Indemnification assets acquired	20,700	20,700
Compensation related payments	10,400	10,400
Unrecognized tax benefits	4,900	4,900
Chargeback and rebate-related items	5,400	5,400
Measurement Period Adjustments
Accounts receivable, net of revenue-related reserves					(19,801)
Inventories					194
Other current assets					(1,635)
Property, plant and equipment					14,431
In-process research and development					(107,000)
Goodwill					98,850
Deferred tax assets					(770)
Other assets					5,359
Total assets acquired					6,628
Accrued expenses					(1,918)
Accrued payroll and payroll-related expenses					(309)
Royalties payable					(196)
Total net assets acquired					(4,597)
Working capital adjustments			4,600
Measurement-period adjustment to returns reserve			6,000
Unaudited Pro Forma Financial Results
Net sales				$ 183,966
Net income attributable to Lannett Company, Inc.				$ 26,136
Earnings per common share attributable to Lannett Company, Inc.:
Basic				$ 0.72
Diluted				$ 0.70
Proforma earnings				$ 26,136
KUPI | Scenario, Previously Reported
Purchase price allocation of the assets acquired and liabilities assumed
Cash and cash equivalents	16,877	16,877
Accounts receivable, net of revenue-related reserves	149,209	149,209
Inventories	83,815	83,815
Other current assets	12,873	12,873
Property, plant and equipment	97,418	97,418
In-process research and development	232,000	232,000
Goodwill	240,575	240,575
Deferred tax assets	4,956	4,956
Other assets	4,859	4,859
Total assets acquired	1,274,502	1,274,502
Accounts payable	(19,249)	(19,249)
Accrued expenses	(4,161)	(4,161)
Accrued payroll and payroll-related expenses	(20,731)	(20,731)
Rebates payable	(9,816)	(9,816)
Royalties payable	(3,798)	(3,798)
Other liabilities	(5,369)	(5,369)
Total net assets acquired	$ 1,211,378	1,211,378
KUPI | Acquisition-related Costs
Unaudited Pro Forma Financial Results
Net income attributable to Lannett Company, Inc.				5,600
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings				5,600
KUPI | Acquisition costs incurred by acquirer
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses				3,900
KUPI | Acquisition costs incurred by acquiree
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses				$ 1,700
KUPI | Fair value set-up adjustment
Purchase price allocation of the assets acquired and liabilities assumed
Inventory fair value step-up adjustments		$ 19,100
Senior Notes due 2023
Fair value of total consideration transferred:
Debt instrument, stated percentage	12.00%	12.00%
Aggregate principal amount	$ 250,000	$ 250,000
Revolving Credit Facility
Fair value of total consideration transferred:
Aggregate principal amount	22,800	22,800
Term loans
Fair value of total consideration transferred:
Aggregate principal amount	910,000	910,000
Product rights | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets			427,000		427,000
Measurement Period Adjustments
Intangible assets					18,000
Product rights | KUPI | Scenario, Previously Reported
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets	409,000	409,000
Trade name | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets			2,920		2,920
Trade name | KUPI | Scenario, Previously Reported
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets	2,920	2,920
Other Intangible Assets | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets			$ 19,000		19,000
Measurement Period Adjustments
Intangible assets					$ (1,000)
Other Intangible Assets | KUPI | Scenario, Previously Reported
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets	$ 20,000	$ 20,000