Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended			6 Months Ended
	Nov. 25, 2015	Nov. 25, 2015	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	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
Net sales			170,944		$ 127,059	332,503	$ 233,492
Net loss attributable to Lannett Company, Inc.			$ 8,172		$ 13,520	$ (21,236)	$ 46,701
Loss per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)			$ 0.22		$ 0.37	$ (0.58)	$ 1.28
Diluted (in dollars per share)			$ 0.22		$ 0.36	$ (0.58)	$ 1.25
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 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%	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
Measurement-period adjustment to returns reserve				$ 6,000
Unaudited Pro Forma Financial Results
Revenues					$ 173,189		$ 357,155
Net income attributable to Lannett Company, Inc.					$ 28,810		$ 55,129
Earnings per common share attributable to Lannett Company, Inc.:
Basic					$ 0.79		$ 1.52
Diluted					$ 0.77		$ 1.47
Proforma earnings					$ 28,810		$ 55,129
KUPI | Acquisition-related Costs
Unaudited Pro Forma Financial Results
Net income attributable to Lannett Company, Inc.					23,300		28,900
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings					23,300		28,900
KUPI | Acquisition costs incurred by acquirer
Purchase price allocation of the assets acquired and liabilities assumed
Business Combination, Acquisition Related Costs					17,600		21,500
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					17,600		21,500
KUPI | Acquisition costs incurred by acquiree
Purchase price allocation of the assets acquired and liabilities assumed
Business Combination, Acquisition Related Costs					5,700		7,400
Earnings per common share attributable to Lannett Company, Inc.:
Acquisition-related expenses					5,700		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.					5,800		5,800
Earnings per common share attributable to Lannett Company, Inc.:
Proforma earnings					$ 5,800		$ 5,800
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
Trade name | KUPI
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