STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Product revenue, net	$ 159,201,000	$ 81,321,000	$ 50,286,000
Operating expenses:
Cost of sales	3,554,000	2,058,000	1,361,000
Research and development	40,376,000	23,844,000	15,419,000
Selling, general and administrative	62,416,000	45,240,000	36,949,000
Total operating expenses	106,346,000	71,142,000	53,729,000
Income (loss) from operations	52,855,000	10,179,000	(3,443,000)
Interest and other expense	(49,000)	(2,039,000)	(2,965,000)
Income before income taxes	52,806,000	8,140,000	(6,408,000)
Income tax benefit	76,316,000	0	0
Net income (loss)	129,122,000	8,140,000	(6,408,000)
Other comprehensive income (loss):
Net unrealized loss on available-for-sale investments	(75,000)	0	0
Total comprehensive income (loss)	$ 129,047,000	$ 8,140,000	$ (6,408,000)
Basic net income (loss) per common share	$ 1.14	$ 0.07	$ (0.06)
Diluted net income (loss) per common share	$ 1.04	$ 0.07	$ (0.06)
Weighted average shares outstanding used in computing net income (loss) per share
Basic	113,527	110,566	106,883
Diluted	124,515	116,139	106,883