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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
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost $ 92,416 $ 100,990
Unrealized Gains (Losses) 36 (236)
Accrued Interest 226 280
Estimated Fair Value 92,678 101,034
Cash & Cash Equivalents 76,974 81,364
Investment Securities 15,704 19,670
Cash [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 36,593 35,436
Estimated Fair Value 36,593 35,436
Cash & Cash Equivalents 36,593 35,436
Fair Value, Inputs, Level 1 [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 43,213 48,763
Unrealized Gains (Losses) 2 (72)
Estimated Fair Value 43,215 48,691
Cash & Cash Equivalents 40,381 45,928
Investment Securities 2,834 2,763
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 35,000 40,000
Estimated Fair Value 35,000 40,000
Cash & Cash Equivalents 35,000 40,000
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 5,381 5,928
Estimated Fair Value 5,381 5,928
Cash & Cash Equivalents 5,381 5,928
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 2,832 2,835
Unrealized Gains (Losses) 2 (72)
Estimated Fair Value 2,834 2,763
Investment Securities 2,834 2,763
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 12,610 16,791
Unrealized Gains (Losses) 34 (164)
Accrued Interest 226 280
Estimated Fair Value 12,870 16,907
Investment Securities $ 12,870 $ 16,907