SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Fair Value Measurements (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value Measurements [Abstract]
Unrealized gains (losses) on investments	$ 0	$ 0
Amortized premium included in interest income	327,000	610,000
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	45,115,391	44,254,862
Held-to-maturity securities, noncurrent	7,396,902	3,771,380
Recurring [Member] | Institutional Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,973,534	2,290,331
Recurring [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	5,091,468	7,554,028
Recurring [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	43,248,481	33,354,407
Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	4,172,344	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	2,973,534	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	4,172,344	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	5,091,468	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	43,248,481	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	5,091,468	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	35,851,579	30,418,120
Held-to-maturity securities, noncurrent	7,396,902	2,936,287
Certificates of Deposit [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, current	4,172,344	6,868,788
Held-to-maturity securities, noncurrent	$ 0	$ 249,019