Selected Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Product revenues	$ 617,000	$ 709,000	$ 856,000	$ 1,301,000	$ 2,045,000	$ 2,251,000	$ 3,116,000	$ 2,610,000	$ 3,483,000	$ 10,022,000	$ 12,917,000
Research and development programs	4,219,000	3,601,000	3,592,000	3,587,000	3,348,000	2,266,000	3,433,000	3,784,000	14,999,000	12,831,000	23,045,000
Total revenues	4,836,000	4,310,000	4,448,000	4,888,000	5,393,000	4,517,000	6,549,000	6,394,000	18,482,000	22,853,000	35,962,000
Costs and operating expenses:
Cost of product revenues	2,218,000	884,000	850,000	1,304,000	2,788,000	2,411,000	3,014,000	2,350,000	5,256,000	10,563,000	12,866,000
Research and development	6,901,000	7,708,000	8,276,000	8,231,000	9,586,000	13,207,000	12,747,000	12,554,000	31,116,000	48,094,000	81,680,000
Sales, general and administrative	10,096,000	11,169,000	10,834,000	11,642,000	14,075,000	15,143,000	16,411,000	16,412,000	43,741,000	62,041,000	72,621,000
Restructuring charges	(43,000)	216,000	49,000	1,190,000	4,581,000	(21,000)	(31,000)	424,000	1,412,000	4,953,000	3,514,000
Total costs and operating expenses	19,172,000	19,977,000	20,009,000	22,367,000	31,030,000	30,740,000	32,141,000	31,740,000	81,525,000	125,651,000	170,681,000
Loss from continuing operations before other income (expense):	(14,336,000)	(15,667,000)	(15,561,000)	(17,479,000)	(25,637,000)	(26,223,000)	(25,592,000)	(25,346,000)	(63,043,000)	(102,798,000)	(134,719,000)
Other income (expense):
Interest and other income, net	(2,544,000)	(2,898,000)	(3,157,000)	(3,116,000)	(3,314,000)	(3,047,000)	(3,534,000)	(3,300,000)
Loss from equity method investments	(5,783,000)	(6,378,000)	(5,358,000)	(4,872,000)	(4,098,000)	(5,916,000)	(7,309,000)	(5,066,000)	(22,391,000)	(22,389,000)	(23,037,000)
Debt conversion expense	(4,743,000)	(3,242,000)	(1,785,000)	0	0	0	0	0	(9,770,000)	0	(1,766,000)
Total other expense, net	(13,070,000)	(12,518,000)	(10,300,000)	(7,988,000)	(7,412,000)	(8,963,000)	(10,843,000)	(8,366,000)	(43,876,000)	(35,584,000)	(26,442,000)
Loss from continuing operations before income taxes	(27,406,000)	(28,185,000)	(25,861,000)	(25,467,000)	(33,049,000)	(35,186,000)	(36,435,000)	(33,712,000)	(106,919,000)	(138,382,000)	(161,161,000)
Benefit from income taxes	(223,000)	(1,839,000)	0	0	0	0	0	0	(2,062,000)	0	0
Loss from continuing operations	(27,183,000)	(26,346,000)	(25,861,000)	(25,467,000)	(33,049,000)	(35,186,000)	(36,435,000)	(33,712,000)	(104,857,000)	(138,382,000)	(161,161,000)
Income (loss) from discontinued operations	71,000	5,852,000	(1,577,000)	(1,045,000)	(1,644,000)	268,000	(736,000)	(953,000)	3,301,000	(3,065,000)	(980,000)
Net loss	$ (27,112,000)	$ (20,494,000)	$ (27,438,000)	$ (26,512,000)	$ (34,693,000)	$ (34,918,000)	$ (37,171,000)	$ (34,665,000)	$ (101,556,000)	$ (141,447,000)	$ (162,141,000)
Net income (loss) per share from continuing operations, per basic and diluted share (in dollars per share)	$ (0.30)	$ (0.31)	$ (0.31)	$ (0.31)	$ (0.41)	$ (0.44)	$ (0.45)	$ (0.43)	$ (1.22)	$ (1.73)	$ (2.13)
Net income (loss) from discontinued operations, per basic and diluted share (in dollars per share)	0.00	0.07	(0.02)	(0.01)	(0.02)	0.01	(0.01)	(0.01)	0.04	(0.03)	(0.01)
Net loss per share, basic and diluted (in dollars per share)	$ (0.30)	$ (0.24)	$ (0.33)	$ (0.32)	$ (0.43)	$ (0.43)	$ (0.46)	$ (0.44)	$ (1.18)	$ (1.76)	$ (2.14)
Weighted-average number of shares used in loss per share computation:
Basic and diluted (in shares)	91,582	85,837	84,380	81,950	80,600	80,298	80,098	79,650	85,952	80,165	75,879