Business and Significant Accounting Policies (Details) (USD $)	12 Months Ended		1 Months Ended
	Dec. 31, 2012 Y M bmi item	Dec. 31, 2011	Nov. 30, 2010 Deerfield ED Corp.
Business
BMI of patients to discuss safety and efficacy of Qnexa, one	30
BMI of patients to discuss safety and efficacy of Qnexa, two	27
Minimum number of weight-related comorbidity considered to discuss safety and efficacy of Qnexa	1
Number of previously approved drugs from which low doses of active ingredients incorporated	2
Number of main mechanisms that impact eating behavior	2
Accumulated deficit	$ (486,146,000)	$ (346,265,000)
Principles of Consolidation
Percentage of ownership acquired in subsidiary			100.00%
Available-for-Sale Securities
Minimum maturity period for available-for-sale securities (in months)	12
Minimum maturity period for available-for-sale securities to support current operations securities to classify as current assets (in months)	12
Fair Value Measurements
Cash and cash equivalents and available-for-sale securities measured at fair value on a recurring basis	214,586,000	146,836,000
Period within which valuation techniques used to measure fair values of financial instruments (in years)	1
Accounts Receivable, Allowances for Doubtful Accounts and Cash Discounts
Cash discount (as a percent)	2.00%
Allowance for cash discounts	$ 57,000	$ 0
Property and Equipment
Estimated useful lives for computers and software and furniture and fixtures, minimum (in years)	2
Estimated useful lives for computers and software and furniture and fixtures, maximum (in years)	7