Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CASH FLOW FROM OPERATING ACTIVITIES
Net loss	$ (88,929)	$ (60,542)	$ (46,090)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,009	827	671
Gain on sale of assets, net	(3,334)	(3,222)	(3,170)
Cease-use expense	(85)	0	0
Deferred revenues	10,231	0	(2,919)
Deferred rent	(16)	14	142
Amortization of premiums on investments	6,032	3,792	2,843
Non-cash share-based compensation expense	28,392	10,382	6,819
Change in operating assets and liabilities:
Accounts receivable and other assets	(489)	(1,671)	13,528
Cease-use liability	(610)	(418)	(590)
Other liabilities	(39)	0	108
Accounts payable and accrued liabilities	9,841	3,698	(949)
Net cash used in operating activities	(37,997)	(47,140)	(29,607)
CASH FLOW FROM INVESTING ACTIVITIES
Purchases of investments	(449,052)	(257,544)	(145,328)
Sales/maturities of investments	255,123	154,133	151,281
Deposits and restricted cash	40	(388)	(108)
Proceeds from sales of property and equipment	9	45	40
Purchases of property and equipment	(1,934)	(1,612)	(545)
Net cash (used in) provided by investing activities	(195,814)	(105,366)	5,340
CASH FLOW FROM FINANCING ACTIVITIES
Issuance of common stock	276,992	138,731	5,302
Net cash provided by financing activities	276,992	138,731	5,302
Net change in cash and cash equivalents	43,181	(13,775)	(18,965)
Cash and cash equivalents at beginning of the year	31,014	44,789	63,754
Cash and cash equivalents at end of the year	74,195	31,014	44,789
SUPPLEMENTAL DISCLOSURES
Taxes paid	$ 0	$ 0	$ 0