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, 2020	Dec. 31, 2019
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	$ 174,241	$ 92,416
Unrealized Gains	87	36
Accrued Interest	147	226
Estimated Fair Value	174,475	92,678
Cash & Cash Equivalents	163,723	76,974
Investment Securities	10,752	15,704
Cash [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	159,754	36,593
Estimated Fair Value	159,754	36,593
Cash & Cash Equivalents	159,754	36,593
Fair Value, Inputs, Level 1 [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	6,798	43,213
Unrealized Gains	45	2
Estimated Fair Value	6,843	43,215
Cash & Cash Equivalents	3,969	40,381
Investment Securities	2,874	2,834
Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost		35,000
Estimated Fair Value		35,000
Cash & Cash Equivalents		35,000
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	3,969	5,381
Estimated Fair Value	3,969	5,381
Cash & Cash Equivalents	3,969	5,381
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	2,829	2,832
Unrealized Gains	45	2
Estimated Fair Value	2,874	2,834
Investment Securities	2,874	2,834
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	7,689	12,610
Unrealized Gains	42	34
Accrued Interest	147	226
Estimated Fair Value	7,878	12,870
Investment Securities	$ 7,878	$ 12,870