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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
Jun. 30, 2019
Dec. 31, 2018
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost $ 113,262 $ 100,990
Unrealized Losses (9) (236)
Accrued Interest 269 280
Estimated Fair Value 113,522 101,034
Cash & Cash Equivalents 96,311 81,364
Investment Securities 17,211 19,670
Cash [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 32,632 35,436
Estimated Fair Value 32,632 35,436
Cash & Cash Equivalents 32,632 35,436
Fair Value, Inputs, Level 1 [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 66,512 48,763
Unrealized Losses (9) (72)
Accrued Interest 23  
Estimated Fair Value 66,526 48,691
Cash & Cash Equivalents 63,679 45,928
Investment Securities 2,847 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 3,679 5,928
Estimated Fair Value 3,679 5,928
Cash & Cash Equivalents 3,679 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 (9) (72)
Accrued Interest 23  
Estimated Fair Value 2,847 2,763
Investment Securities 2,847 2,763
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 14,118 16,791
Unrealized Losses   (164)
Accrued Interest 246 280
Estimated Fair Value 14,364 16,907
Investment Securities $ 14,364 $ 16,907