Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Product, net	$ 78,486	$ 45,954	$ 216,619	$ 97,307
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 78,486	$ 45,954	$ 216,619	$ 97,307
Costs and expenses:
Cost of sales (excluding amortization of in-licensed rights)	8,741	3,078	21,058	3,807
Research and development	86,584	34,239	255,636	122,266
Selling, general and administrative	53,044	28,176	143,541	90,461
EXONDYS 51 litigation and license charges		25,588		28,427
Amortization of in-licensed rights	216	780	649	837
Total costs and expenses	148,585	91,861	420,884	245,798
Operating loss	(70,099)	(45,907)	(204,265)	(148,491)
Other (loss) income:
Gain from sale of Priority Review Voucher				125,000
Interest (expense) income and other, net	(6,968)	184	(16,671)	703
Other (loss) income	(6,968)	184	(16,671)	125,703
Loss before income tax (benefit) expense	(77,067)	(45,723)	(220,936)	(22,788)
Income tax (benefit) expense	(674)	2,011	87	3,902
Net loss	(76,393)	(47,734)	(221,023)	(26,690)
Other comprehensive income:
Unrealized gain on cash equivalents and short-term investments	369	26	387	108
Total other comprehensive income	369	26	387	108
Comprehensive loss	$ (76,024)	$ (47,708)	$ (220,636)	$ (26,582)
Net loss per share - basic and diluted	$ (1.15)	$ (0.78)	$ (3.38)	$ (0.47)
Weighted average number of shares of common stock used in computing basic and diluted net loss per share	66,209	61,528	65,454	57,166