Fair Value Measurements - Available-for-Sale Securities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Assets:
Restricted cash	$ 700	$ 700
Short-term investments		491
Total available-for-sale securities	99,993	202,839
Equity securities	39,309	35,285
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	424,464	229,218
Restricted cash	700	700
Short-term investments		491
Total available-for-sale securities	99,993	202,839
Equity securities	39,309	35,285
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Financial Assets:
Cash and cash equivalents	424,464	229,218
Restricted cash	700	700
Short-term investments		491
Total available-for-sale securities	92,541	193,926
Equity securities	39,309	35,285
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member]
Financial Assets:
Total available-for-sale securities	7,452	8,913
U.S. Treasury and U.S. Government Agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Total available-for-sale securities	12,442	26,295
U.S. Treasury and U.S. Government Agencies [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Financial Assets:
Total available-for-sale securities	10,899	25,294
U.S. Treasury and U.S. Government Agencies [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member]
Financial Assets:
Total available-for-sale securities	1,543	1,001
Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Total available-for-sale securities	74,409	159,364
Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Financial Assets:
Total available-for-sale securities	74,409	159,364
State, Municipalities, and Political Subdivisions [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Total available-for-sale securities	5,909	7,912
State, Municipalities, and Political Subdivisions [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member]
Financial Assets:
Total available-for-sale securities	5,909	7,912
Exchange-Traded Debt [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Total available-for-sale securities	7,200	9,145
Exchange-Traded Debt [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Financial Assets:
Total available-for-sale securities	7,200	9,145
Redeemable Preferred Stock [Member] \| Fair Value, Measurements, Recurring [Member]
Financial Assets:
Total available-for-sale securities	33	123
Redeemable Preferred Stock [Member] \| Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Financial Assets:
Total available-for-sale securities	$ 33	$ 123

Disclosure fair value of financial assets.

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Represents investments in certificates of deposit and commercial paper with original maturities of more than three months but less than one year at date of acquisition.

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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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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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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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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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