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, 2020	Dec. 31, 2019
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	$ 145,087	$ 92,416
Unrealized Gains	113	36
Accrued Interest	192	226
Estimated Fair Value	145,392	92,678
Cash & Cash Equivalents	130,828	76,974
Investment Securities	14,564	15,704
Cash [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	130,733	36,593
Estimated Fair Value	130,733	36,593
Cash & Cash Equivalents	130,733	36,593
Fair Value, Inputs, Level 1 [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	2,925	43,213
Unrealized Gains	63	2
Estimated Fair Value	2,988	43,215
Cash & Cash Equivalents	95	40,381
Investment Securities	2,893	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	95	5,381
Estimated Fair Value	95	5,381
Cash & Cash Equivalents	95	5,381
Fair Value, Inputs, Level 1 [Member] | Government and Agency Securities [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	2,830	2,832
Unrealized Gains	63	2
Estimated Fair Value	2,893	2,834
Investment Securities	2,893	2,834
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Cash And Cash Equivalents And Marketable securities [Line Items]
Cost	11,429	12,610
Unrealized Gains	50	34
Accrued Interest	192	226
Estimated Fair Value	11,671	12,870
Investment Securities	$ 11,671	$ 12,870