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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
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost $ 197,311 $ 174,241
Unrealized Gains 54 87
Accrued Interest 62 147
Estimated Fair Value 197,427 174,475
Cash & Cash Equivalents 191,987 163,723
Investment Securities 5,440 10,752
Cash [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 182,694 159,754
Estimated Fair Value 182,694 159,754
Cash & Cash Equivalents 182,694 159,754
Fair Value, Inputs, Level 1 [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 10,696 6,798
Unrealized Gains 26 45
Estimated Fair Value 10,722 6,843
Cash & Cash Equivalents 9,293 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 9,293 3,969
Estimated Fair Value 9,293 3,969
Cash & Cash Equivalents 9,293 3,969
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]    
Cash And Cash Equivalents And Marketable securities [Line Items]    
Cost 1,403 2,829
Unrealized Gains 26 45
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 3,921 7,689
Unrealized Gains 28 42
Accrued Interest 62 147
Estimated Fair Value 4,011 7,878
Investment Securities $ 4,011 $ 7,878