Investments - Schedule of Available-for-sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Short-Term Marketable Securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	$ 540,016	$ 564,036
Unrealized Gain	624	809
Unrealized Loss		(12)
Estimated Fair Value	540,640	564,833
Long-Term Marketable Securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	30,681	118,429
Unrealized Gain	10	98
Unrealized Loss	(3)	(2)
Estimated Fair Value	30,688	118,525
U.S. Government Debt Securities | Short-Term Marketable Securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	528,522	552,539
Unrealized Gain	578	723
Unrealized Loss		(10)
Estimated Fair Value	529,100	553,252
U.S. Government Debt Securities | Long-Term Marketable Securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	30,681	118,429
Unrealized Gain	10	98
Unrealized Loss	(3)	(2)
Estimated Fair Value	30,688	118,525
Corporate Bonds | Short-Term Marketable Securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	11,494	11,497
Unrealized Gain	46	86
Unrealized Loss		(2)
Estimated Fair Value	$ 11,540	$ 11,581