Equity Plan - Information Related to the Equity Plans for each of the Last Three Years (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Information Related to the Equity Plans
Proceeds from issuance of common stock, net of issuance costs	$ 1,368,000	$ 938,000	$ 315,000
Options
Information Related to the Equity Plans
Intrinsic value of options exercised	1,342,794	606,359	216,681
Proceeds from issuance of common stock, net of issuance costs	1,368,673	938,057	315,076
Tax benefit realized from option exercises	$ 547,817	$ 242,303	$ 85,411
Weighted average fair value of options granted (in dollars per share)	$ 2.66	$ 2.12	$ 3.15