Fortress Biotech, Inc. Quarterly report pursuant to Section 13 or 15(d)

Fair Value Hierarchy Financial Instruments Measured at Fair Value on Recurring Basis (Detail)

Fair Value Hierarchy Financial Instruments Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments, at fair value	$ 3,945	$ 4,160
Trading Securities	20,005us-gaap_TradingSecurities	20,002us-gaap_TradingSecurities
Total	23,950us-gaap_MarketableSecurities	24,162us-gaap_MarketableSecurities
U.S. Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	20,000	19,998
Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	5	4
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments, at fair value	0	0
Trading Securities	20,005	20,002
Total	20,005	20,002
Fair Value, Inputs, Level 1 [Member] \| U.S. Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	20,000	19,998
Fair Value, Inputs, Level 1 [Member] \| Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	5	4
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments, at fair value	0	0
Trading Securities	0	0
Total	0	0
Fair Value, Inputs, Level 2 [Member] \| U.S. Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Fair Value, Inputs, Level 2 [Member] \| Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-Term Investments, at fair value	3,945	4,160
Trading Securities	0	0
Total	3,945	4,160
Fair Value, Inputs, Level 3 [Member] \| U.S. Treasury Bills [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Fair Value, Inputs, Level 3 [Member] \| Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	$ 0	$ 0