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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
Sep. 30, 2019
Dec. 31, 2018
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost $ 96,737 $ 100,990
Unrealized Losses 10 (236)
Accrued Interest 167 280
Estimated Fair Value 96,914 101,034
Cash & Cash Equivalents 81,196 81,364
Investment Securities 15,718 19,670
Cash [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 75,930 35,436
Estimated Fair Value 75,930 35,436
Cash & Cash Equivalents 75,930 35,436
Fair Value, Inputs, Level 1 [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 8,098 48,763
Unrealized Losses (1) (72)
Accrued Interest 11  
Estimated Fair Value 8,108 48,691
Cash & Cash Equivalents 5,266 45,928
Investment Securities 2,842 2,763
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost   40,000
Estimated Fair Value   40,000
Cash & Cash Equivalents   40,000
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 5,266 5,928
Estimated Fair Value 5,266 5,928
Cash & Cash Equivalents 5,266 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 Losses (1) (72)
Accrued Interest 11  
Estimated Fair Value 2,842 2,763
Investment Securities 2,842 2,763
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 12,709 16,791
Unrealized Losses 11 (164)
Accrued Interest 156 280
Estimated Fair Value 12,876 16,907
Investment Securities $ 12,876 $ 16,907