Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			9 Months Ended
	Nov. 25, 2015	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Mar. 31, 2016	Dec. 31, 2016	Jun. 30, 2016
Fair value of total consideration transferred:
Acquisition-related contingent consideration					$ 35,000
Payment to UCB for tax liability		$ 35,000
Purchase price allocation of the assets acquired and liabilities assumed
Goodwill		$ 339,566					$ 333,611
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
Working capital adjustment	(41,605)
Certain amounts reimbursable 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%
Business combination recognized identifiable assets acquired and liabilities assumed cash on hand	$ 94,600
Additional tax benefits	100,000
Purchase price allocation of the assets acquired and liabilities assumed
Cash and cash equivalents						$ 16,877
Accounts receivable, net of revenue-related reserves						129,408
Inventories						84,009
Other current assets						11,238
Property, plant and equipment						111,849
In-process research and development						125,000
Goodwill						339,425
Deferred tax assets						4,186
Other assets						10,218
Total assets acquired						1,281,130
Accounts payable						(19,249)
Accrued expenses						(6,079)
Accrued payroll and payroll-related expenses						(21,040)
Rebates payable						(9,816)
Royalties payable						(3,602)
Other liabilities						(5,369)
Total net assets acquired						1,215,975
Indemnification assets acquired	20,700
Compensation related payments	10,400
Unrecognized tax benefits	4,900
Chargeback and rebate-related items	5,400
Measurement Period Adjustments
Measurement-period adjustment to returns reserve			$ 6,000
Unaudited Pro Forma Financial Results
Revenues				$ 163,712	520,867
Net income attributable to Lannett Company, Inc.				$ 896	$ 55,596
Earnings per common share attributable to Lannett Company, Inc.:
Basic				$ 0.02	$ 1.53
Diluted				$ 0.02	$ 1.49
Proforma earnings				$ 896	$ 55,596
KUPI | Acquisition-related Costs
Unaudited Pro Forma Financial Results
Net income attributable to Lannett Company, Inc.				8,600	28,900
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings				$ 8,600	28,900
KUPI | Acquisition costs incurred by acquirer
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					21,500
KUPI | Acquisition costs incurred by acquiree
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					7,400
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.					14,400
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings					$ 14,400
Senior Notes due 2023
Fair value of total consideration transferred:
Debt instrument, stated percentage	12.00%
Aggregate principal amount	$ 250,000
Revolving Credit Facility
Fair value of total consideration transferred:
Aggregate principal amount	22,800
Term loans
Fair value of total consideration transferred:
Aggregate principal amount	$ 910,000
Product rights | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets						427,000
Trade name | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets						2,920
Other Intangible Assets | KUPI
Purchase price allocation of the assets acquired and liabilities assumed
Intangible assets						$ 19,000