Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss	$ 512,256	$ 882,014
Tax credit carryforwards	549,543	487,635
Intangible assets	275,290	241,775
Deferred revenues	18,833	19,311
Stock-based compensation	85,199	93,915
Accrued expenses	44,367	17,795
Finance lease liabilities	119,160	130,849
Operating lease assets	13,114
Other	8,596	6,831
Gross deferred tax assets	1,626,358	1,880,125
Valuation allowance	(205,192)	(168,491)
Total deferred tax assets	1,421,166	1,711,634
Deferred tax liabilities:
Property and equipment	(101,235)	(128,407)
Acquired intangibles	(87,160)	0
Deferred revenue	0	(73,357)
Unrealized gain	(28,838)	(10,198)
Operating lease liabilities	(13,118)
Unrealized gain	$ 1,190,815	$ 1,499,672