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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	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	$ 120,342	$ 100,990
Unrealized Losses	(109)	(236)
Accrued Interest	194	280
Estimated Fair Value	120,427	101,034
Cash & Cash Equivalents	101,842	81,364	$ 86,963	$ 75,077
Investment Securities	18,585	19,670
Cash [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	39,714	35,436
Estimated Fair Value	39,714	35,436
Cash & Cash Equivalents	39,714	35,436
Fair Value, Inputs, Level 1 [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	64,961	48,763
Unrealized Losses	(48)	(72)
Accrued Interest	11
Estimated Fair Value	64,924	48,691
Cash & Cash Equivalents	62,128	45,928
Investment Securities	2,796	2,763
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	60,000	40,000
Estimated Fair Value	60,000	40,000
Cash & Cash Equivalents	60,000	40,000
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	2,128	5,928
Estimated Fair Value	2,128	5,928
Cash & Cash Equivalents	2,128	5,928
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	2,833	2,835
Unrealized Losses	(48)	(72)
Accrued Interest	11
Estimated Fair Value	2,796	2,763
Investment Securities	2,796	2,763
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	15,667	16,791
Unrealized Losses	(61)	(164)
Accrued Interest	183	280
Estimated Fair Value	15,789	16,907
Investment Securities	$ 15,789	$ 16,907

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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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