Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income (loss)	$ (51,802,000)	$ 10,223,000	$ 50,921,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Depreciation and amortization	435,000	155,000	66,000
Stock-based compensation	9,956,000	7,203,000	640,000
Excess tax benefit on the exercise of stock options		(1,599,000)
Change in preferred stock warrant value		983,000	4,526,000
Net accretion of discounts and amortization of premiums of available-for-sale securities	875,000	(1,361,000)
Issuance of common stock and vesting of restricted common stock for services rendered			52,000
Loss on fixed asset disposal		111,000
Changes in assets and liabilities
Accrued interest of available-for-sale securities	110,000
Prepaid expenses and other assets	(4,416,000)	(381,000)	80,000
Accounts receivable	(760,000)	(395,000)	761,000
Accounts payable	(788,000)	1,521,000	(1,157,000)
Deferred revenue			(29,611,000)
Accrued liabilities and other liabilities	(820,000)	9,734,000	523,000
Net cash provided by (used in) operating activities	(47,210,000)	26,194,000	26,801,000
Cash flows from investing activities
Purchases of property and equipment	(1,399,000)	(1,285,000)	(167,000)
Purchases of available-for-sale securities	(59,828,000)	(96,095,000)
Maturities of available-for-sale securities	69,285,000
Net cash provided by (used in) investing activities	8,058,000	(97,380,000)	(167,000)
Cash flows from financing activities
Proceeds from public offerings, net of offering costs	9,657,000	42,632,000
Proceeds from issuance of common stock upon exercise of stock options	746,000	1,011,000	21,000
Proceeds from employee stock purchase plan	407,000	162,000
Excess tax benefit on the exercise of stock options		1,599,000
Principal payments on convertible promissory notes			(4,000,000)
Repurchase of common stock		(370,000)
Proceeds from issuance of common and preferred stock upon exercise of warrants		1,986,000
Net cash provided by financing activities	10,810,000	47,020,000	(3,979,000)
Net increase (decrease) in cash and cash equivalents	(28,342,000)	(24,166,000)	22,655,000
Cash and cash equivalents at beginning of period	61,446,000	85,612,000	62,957,000
Cash and cash equivalents at end of period	33,104,000	61,446,000	85,612,000
Supplemental disclosure
Cash paid for income taxes	4,691,000	$ 341,000	1,417,000
Cash paid for interest			$ 279,000
Supplemental disclosure of noncash investing and financing activities
Purchases of property and equipment included in accrued expense	$ 161,000