Income Taxes (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Income tax expense at the statutory federal income tax rate	$ 8,078,000	$ 9,065,000	$ 8,828,000
Increase (decrease) resulting from:
State income taxes	838,000	978,000	1,572,000
R&D tax credits	(1,589,000)	(1,470,000)	(1,212,000)
Foreign-derived intangible income deduction	(1,051,000)	(1,700,000)	(1,000,000)
Excess tax benefit from stock compensation	(81,000)	(412,000)	(95,000)
Change in valuation allowance	(13,000)	(16,000)	0
Uncertain tax positions	(450,000)	(42,000)	(373,000)
Other, net	619,000	4,000	61,000
Provision for Income Taxes	$ 6,352,000	$ 6,407,000	$ 7,781,000