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Financial Instruments (Cash and Available for Sale Securities Adjusted Cost, Gross Unrealized Gains, Gross Unrealized Losses, and Fair Value by Significant Investment Category) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	$ 159,819	$ 174,241
Unrealized Gains	37	87
Accrued Interest	39	147
Estimated Fair Value	159,895	174,475
Cash & Cash Equivalents	154,516	163,723
Investment Securities	5,379	10,752
Cash [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	145,166	159,754
Estimated Fair Value	145,166	159,754
Cash & Cash Equivalents	145,166	159,754
Fair Value, Inputs, Level 1 [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	10,752	6,798
Unrealized Gains	19	45
Accrued Interest	8
Estimated Fair Value	10,779	6,843
Cash & Cash Equivalents	9,350	3,969
Investment Securities	1,429	2,874
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	9,350	3,969
Estimated Fair Value	9,350	3,969
Cash & Cash Equivalents	9,350	3,969
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	1,402	2,829
Unrealized Gains	19	45
Accrued Interest	8
Estimated Fair Value	1,429	2,874
Investment Securities	1,429	2,874
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	3,901	7,689
Unrealized Gains	18	42
Accrued Interest	31	147
Estimated Fair Value	3,950	7,878
Investment Securities	$ 3,950	$ 7,878

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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), classified as current.

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Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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