Cash Equivalents, Marketable Securities and Corporate Equity Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Equity securities included in other non-current assets:
Gross Unrealized Gains	$ 14,525
Cash Equivalents, Marketable Securities and Equity Securities
Amortized Cost	584,012		$ 460,700
Gross Unrealized Gains	14,708		107
Fair Value	598,720		460,807
Realized gains (losses) on available-for-sale securities	0	$ 0
Corporate equity securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	3,667
Gross Unrealized Gains	14,525
Fair Value	18,192
Equity securities included in other non-current assets:
Amortized Cost			3,667
Fair Value			3,667
Money market funds
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	485,819		230,201
Fair Value	485,819		230,201
U.S. Treasuries
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	26,961		71,348
Gross Unrealized Gains	36		20
Fair Value	26,997		71,368
Government agency securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	67,565		155,484
Gross Unrealized Gains	147		87
Fair Value	$ 67,712		$ 155,571

Amortized cost of investments in marketable securities.

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Amount of unrealized gain on investment in marketable security.

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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).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of investment in marketable security.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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