SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Fair Value Measurements (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Measurements [Abstract]
Unrealized gains (losses) on investments	$ 0	$ 0
Amortized premium included in interest income	497,000	610,000
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	48,166,583	44,254,862
Held-to-maturity securities, noncurrent	6,717,196	3,771,380
Recurring [Member] | Institutional Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,565,530	2,290,331
Recurring [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,460,078	7,554,028
Recurring [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	50,353,431	33,354,407
Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	3,070,270	7,117,807
Recurring [Member] | Level 1 [Member] | Institutional Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,565,530	2,290,331
Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring [Member] | Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring [Member] | Level 1 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	3,070,270	7,117,807
Recurring [Member] | Level 2 [Member] | Institutional Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,460,078	7,554,028
Recurring [Member] | Level 2 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	50,353,431	33,354,407
Recurring [Member] | Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring [Member] | Level 3 [Member] | Institutional Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring [Member] | Level 3 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring [Member] | Level 3 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Municipal Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	1,460,078	6,967,954
Held-to-maturity securities, noncurrent	0	586,074
Corporate Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	43,880,944	30,418,120
Held-to-maturity securities, noncurrent	6,472,487	2,936,287
Certificates of Deposit [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	2,825,561	6,868,788
Held-to-maturity securities, noncurrent	$ 244,709	$ 249,019