Income Taxes - Reconciliation of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 610,314	$ 518,620
Accrued expenses	13,482	10,613
Credit carryforwards	120,594	75,879
Stock-based compensation	44,510	35,782
Note hedge	22,742	35,181
Depreciation and amortization	593,348	0
Other	23,183	14,771
Total deferred tax assets	1,428,173	690,846
Less valuation allowance	(1,337,350)	(583,235)
Deferred tax assets net	90,823	107,611
Deferred tax liabilities:
Depreciation and amortization	(22,183)	(20,708)
Convertible notes	(24,887)	(43,616)
Tax effects associated with Topic 606	(23,531)	(53,601)
Other	(1,568)	(1,759)
Net deferred tax assets	$ 18,654
Net deferred tax assets		$ (12,073)