Fair Value Measurements - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 2,566,100
Unrealized Losses	(27,992)
U.S. government notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,080,225
Unrealized Losses	(12,549)
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,223,546
Unrealized Losses	(13,088)
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	262,329
Unrealized Losses	$ (2,355)