Summary of Significant Accounting Policies - Impact of Adopting ASC 606, Balance Sheet Pro-Forma Amounts (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 02, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 218,383		$ 267,107	$ 126,568	$ 159,964
Accounts receivable	34		2,649
Unbilled revenue	2,838		2,580
Contract asset	4,041
Non-cash royalty receivable	16,090
Inventory	368		1,038
Prepaid and other current assets	5,680		2,967
Total current assets	247,434		276,341
Property and equipment, net of accumulated depreciation	12,850		14,538
Other assets	4,681		3,797
Total assets	264,965		294,676
LIABILITIES AND SHAREHOLDERS' DEFICIT
Accounts payable	7,786		8,562
Accrued compensation	5,671		11,473
Other accrued liabilities	23,756		15,767
Current portion of deferred lease incentive	784		784
Current portion of liability related to the sale of future royalties, net	27,619		17,779
Current portion of deferred revenue	611		1,405
Total current liabilities	66,227		55,770
Deferred lease incentive, net of current portion	4,933		5,129
Deferred revenue, net of current portion	81,522		93,752
Convertible 4.5% senior notes, net	2,053		2,050
Liability related to the sale of future royalties, net	142,018		151,634
Other long-term liabilities	4,523		4,236
Total liabilities	301,276		312,571
Shareholders' deficit:
Preferred stock
Common stock	1,330		1,325
Additional paid-in capital	1,015,464		1,009,362
Accumulated deficit	(1,053,105)		(1,028,582)
Total shareholders’ deficit	(36,311)		(17,895)
Total liabilities and shareholders’ deficit	264,965		$ 294,676
Pro forma as if previous accounting was in effect | ASU 2014-09
ASSETS
Cash and cash equivalents	218,383	$ 267,107
Accounts receivable	34	2,649
Unbilled revenue	2,838	2,580
Non-cash royalty receivable	8,875	8,900
Inventory	368	1,038
Prepaid and other current assets	5,680	2,967
Total current assets	236,178	285,241
Property and equipment, net of accumulated depreciation	12,850	14,538
Other assets	4,681	3,797
Total assets	253,709	303,576
LIABILITIES AND SHAREHOLDERS' DEFICIT
Accounts payable	7,786	8,562
Accrued compensation	5,671	11,473
Other accrued liabilities	23,756	15,767
Current portion of deferred lease incentive	784	784
Current portion of liability related to the sale of future royalties, net	27,619	17,779
Current portion of deferred revenue	569	1,446
Total current liabilities	66,185	55,811
Deferred lease incentive, net of current portion	4,933	5,129
Deferred revenue, net of current portion	84,423	88,521
Convertible 4.5% senior notes, net	2,053	2,050
Liability related to the sale of future royalties, net	142,018	151,634
Other long-term liabilities	4,523	4,236
Total liabilities	304,135	307,381
Shareholders' deficit:
Common stock	1,330	1,325
Additional paid-in capital	1,015,464	1,009,362
Accumulated deficit	(1,067,220)	(1,014,492)
Total shareholders’ deficit	(50,426)	(3,805)
Total liabilities and shareholders’ deficit	$ 253,709	$ 303,576