Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax liabilities:
Lease items	$ 2,958	$ 377
Unrealized gain	4,586
Total deferred tax liabilities	7,544	377
Deferred tax assets:
Net operating loss carryforwards	254,601	205,793
Federal and state tax credit carryovers	36,870	32,318
Depreciation	3,773	4,383
Stock-based compensation	14,431	12,803
Tax Credits	36,424	9,008
Debt-related deductions	757	934
Total deferred tax assets	346,856	265,239
Deferred tax assets, net	339,312	264,862
Valuation allowance	(339,312)	(264,862)
Total deferred taxes	$ 0	$ 0