Income Taxes -Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 31, 2004	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Provision for income taxes					$ 51	$ 0	$ 0
Valuation allowance of deferred tax asset		$ 654,298			654,298	914,498
Change in the valuation allowance					(260,200)	(48,100)
Federal operating loss carryforwards		2,000,000			2,000,000
State operating loss carryforwards		2,200,000			2,200,000
Net operating loss carryforwards	$ 216,000
Net operating loss and credit carryforwards, annual use limitation	$ 13,000
Research and development credits		83,461			83,461	$ 77,998
Undistributed earnings from its foreign subsidiaries		0			$ 0
Effective income tax rate					35.00%	35.00%	35.00%
Additional income tax expense or benefit		0			$ 0
Reduction for employee remuneration					301,000
Decrease in valuation allowance					301,000
Provisional amount recorded related to mandatory deemed repatriation of foreign earnings					0
Scenario Forecast
Income Taxes [Line Items]
Effective income tax rate				21.00%
ASU 2016-09
Income Taxes [Line Items]
Attributable to excess tax benefits on stock compensation			$ 10,800
Federal
Income Taxes [Line Items]
Research and development credits		55,100			$ 55,100
Federal research and development credits begin to expire					2024
State
Income Taxes [Line Items]
Research and development credits		$ 28,400			$ 28,400