Financial Instruments (Details) $ in Thousands	12 Months Ended
Dec. 31, 2021 USD ($) position	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	$ 829,896	$ 688,606
Proceeds from investments sold	$ 187,600	30,100
Number of investments, unrealized loss position \| position	61
Unrealized loss position	$ 604,700
Amortized Cost
Less than or equal to one year	274,879
Greater than one year but less than five years	557,304
Total	832,183
Fair Value
Less than or equal to one year	275,331
Greater than or equal to one year but less than five years	554,565
Total	829,896
Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	842,224	713,337
Gross Unrealized Gain	1,342	4,310
Gross Unrealized Loss	(3,629)	(51)
Estimated Fair Value	839,937	717,596
Money market deposits
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	10,041	28,990
Estimated Fair Value	10,041	28,990
U.S. Treasury securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	689,640	594,252
Gross Unrealized Gain	1,081	3,512
Gross Unrealized Loss	(2,624)	(20)
Estimated Fair Value	688,097	597,744
Corporate bonds and notes
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	52,729	12,331
Gross Unrealized Gain		2
Gross Unrealized Loss	(392)	(5)
Estimated Fair Value	52,337	12,328
Municipal securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	89,814	77,764
Gross Unrealized Gain	261	796
Gross Unrealized Loss	(613)	(26)
Estimated Fair Value	89,462	78,534
Cash equivalents \| Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	10,041	28,990
Short-term investments \| Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Estimated Fair Value	$ 829,896	$ 688,606

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).