Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss	$ 882,014	$ 1,004,404
Tax credit carryforwards	487,635	440,429
Intangible assets	241,775	54,091
Deferred revenues	19,311	19,593
Stock-based compensation	93,915	83,196
Accrued expenses	17,795	17,808
Construction financing lease obligation	130,849	109,354
Other	6,831	5,667
Gross deferred tax assets	1,880,125	1,734,542
Valuation allowance	(168,491)	(1,552,942)
Total deferred tax assets	1,711,634	181,600
Deferred tax liabilities:
Property and equipment	(128,407)	(101,019)
Acquired intangibles	0	(6,341)
Deferred revenue	(73,357)	(73,357)
Unrealized gain	(10,198)	(6,401)
Net deferred tax assets	$ 1,499,672	834
Net deferred tax liabilities		$ (5,518)