Summary of Significant Accounting Policies - Impact of Adopting ASC 606, Pro Forma Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 02, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents	$ 345,058		$ 267,107	$ 150,337	$ 159,964
Accounts receivable	19		2,649
Unbilled revenue	522		2,580
Non-cash royalty receivable	7,236
Inventory	1,890		1,038
Prepaid and other current assets	9,893		2,967
Total current assets	364,618		276,341
Property and equipment, net of accumulated depreciation	12,029		14,538
Other assets	4,437		3,797
Total assets	381,084		294,676
LIABILITIES AND SHAREHOLDERS’ EQUITY (DEFICIT)
Accounts payable	12,881		8,562
Accrued compensation	8,524		11,473
Other accrued liabilities	17,865		15,767
Current portion of deferred lease incentive	793		784
Current portion of liability related to the sale of future royalties, net	22,265		17,779
Current portion of deferred revenue	1,020		1,405
Total current liabilities	63,348		55,770
Deferred lease incentive, net of current portion	4,806		5,129			$ 2,000
Deferred revenue, net of current portion	80,751		93,752
Convertible 4.5% senior notes, net	2,057		2,050
Liability related to the sale of future royalties, net	136,701		151,634
Other long-term liabilities	4,231		4,236
Total liabilities	291,894		312,571
Shareholders' deficit:
Preferred stock
Common stock	1,490		1,325
Additional paid-in capital	1,182,429		1,009,362
Accumulated deficit	(1,094,729)		(1,028,582)
Total shareholders’ equity (deficit)	89,190		(17,895)
Total liabilities and shareholders’ equity (deficit)	381,084		$ 294,676
Pro forma as if previous accounting was in effect | ASU 2014-09
ASSETS
Cash and cash equivalents	345,058	$ 267,107
Accounts receivable	19	2,649
Unbilled revenue	522	2,580
Non-cash royalty receivable		8,900
Inventory	1,890	1,038
Prepaid and other current assets	9,893	2,967
Total current assets	357,382	285,241
Property and equipment, net of accumulated depreciation	12,029	14,538
Other assets	4,437	3,797
Total assets	373,848	303,576
LIABILITIES AND SHAREHOLDERS’ EQUITY (DEFICIT)
Accounts payable	12,881	8,562
Accrued compensation	8,524	11,473
Other accrued liabilities	17,865	15,767
Current portion of deferred lease incentive	793	784
Current portion of liability related to the sale of future royalties, net	22,265	17,779
Current portion of deferred revenue	755	1,446
Total current liabilities	63,083	55,811
Deferred lease incentive, net of current portion	4,806	5,129
Deferred revenue, net of current portion	83,908	88,521
Convertible 4.5% senior notes, net	2,057	2,050
Liability related to the sale of future royalties, net	136,701	151,634
Other long-term liabilities	4,231	4,236
Total liabilities	294,786	307,381
Shareholders' deficit:
Common stock	1,490	1,325
Additional paid-in capital	1,182,429	1,009,362
Accumulated deficit	(1,104,857)	(1,014,492)
Total shareholders’ equity (deficit)	79,062	(3,805)
Total liabilities and shareholders’ equity (deficit)	$ 373,848	$ 303,576