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

Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Marketable securities, Amortized Cost	$ 20,003us-gaap_TradingSecuritiesCost	$ 20,002us-gaap_TradingSecuritiesCost
Marketable securities, Unrealized Gain	2	0
Marketable securities, Unrealized Loss	0	0
Marketable securities, Fair value	20,005us-gaap_TradingSecurities	20,002us-gaap_TradingSecurities
U.S. treasury bill
Marketable securities, Amortized Cost	19,999	19,998
Marketable securities, Unrealized Gain	1	0
Marketable securities, Unrealized Loss	0	0
Marketable securities, Fair value	20,000	19,998
Mutual fund
Marketable securities, Amortized Cost	4	4
Marketable securities, Unrealized Gain	1	0
Marketable securities, Unrealized Loss	0	0
Marketable securities, Fair value	$ 5	$ 4