Business and Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended					0 Months Ended
	Mar. 31, 2014 Segment	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Accounts Payable [Member]	Apr. 29, 2014 Subsequent Event
Organization And Nature Of Business [Line Items]
Losses incurred during the period	$ 571,509,000	$ 543,236,000
Cash, cash equivalents and investments	233,100,000
Cash and cash equivalents	49,101,000	256,965,000	167,919,000	187,661,000
Short-term investments	176,091,000
Restricted investments	7,900,000
Common stock issued						2,650,000
Common stock offering price per share						$ 38.00
Proceeds from issuance of common stock						94,500,000
Number of operating segments	1
Accrued liabilities	16,340,000	14,601,000			9,600,000
Accrued employee compensation			$ 5,000,000