Investments (Schedule of Amortized Cost, Unrealized Gains and Losses, and Market Value of Investment Securities) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cost	$ 295,692,106	$ 269,889,067
Unrealized Gains	4,899,312	1,974,255
Unrealized Losses	(732,888)	(587,564)
Market Value	299,858,530	271,275,758
Short-Term Investments | Certificates of Deposit
Debt Securities, Available-for-sale [Line Items]
Cost	50,099,795	50,099,795
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	50,099,795	50,099,795
Short-Term Investments | Government Securities
Debt Securities, Available-for-sale [Line Items]
Cost	46,564,204	58,343,911
Unrealized Gains	339,611	99,917
Unrealized Losses	0	(11,005)
Market Value	46,903,815	58,432,823
Short-Term Investments | Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	29,047,745	29,025,624
Unrealized Gains	84,838	194,061
Unrealized Losses	(10,181)	0
Market Value	29,122,402	29,219,685
Short-Term Investments | Other
Debt Securities, Available-for-sale [Line Items]
Cost	2,867,906	2,631,750
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	2,867,906	2,631,750
Short-Term Investments | Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	2,079,998
Unrealized Gains	4,123
Unrealized Losses	0
Market Value	2,084,121
Long-Term Investments | Certificates of Deposit
Debt Securities, Available-for-sale [Line Items]
Cost	5,007,454	3,500,000
Unrealized Gains	87,617	58,808
Unrealized Losses	(8,213)	(1,010)
Market Value	5,086,858	3,557,798
Long-Term Investments | Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Cost	43,046,638	25,971,156
Unrealized Gains	988,808	0
Unrealized Losses	(406,744)	(180,127)
Market Value	43,628,702	25,791,029
Long-Term Investments | Government Securities
Debt Securities, Available-for-sale [Line Items]
Cost	7,150,365	6,012,705
Unrealized Gains	158,219	75,485
Unrealized Losses	0	0
Market Value	7,308,584	6,088,190
Long-Term Investments | Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	20,271,904	22,306,130
Unrealized Gains	330,691	509,868
Unrealized Losses	(205,070)	0
Market Value	20,397,525	22,815,998
Long-Term Investments | Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	89,556,097	71,997,996
Unrealized Gains	2,905,405	1,036,116
Unrealized Losses	(102,680)	(395,422)
Market Value	$ 92,358,822	$ 72,638,690