TAXES - Income Tax Expense and Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
TAXES
Effective tax rate (as a percent)	35.24%	35.19%	32.82%
Colorado ballot initiative costs			$ 1,864
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	$ 12,834	$ 11,968	6,935
State	477	359	46
Current tax provision	13,311	12,327	6,981
Federal	99	(1,117)	637
State	(52)	7	(688)
Deferred Income Tax (benefit) provision	47	(1,110)	(51)
Total tax provision	$ 13,358	$ 11,217	$ 6,930
Income tax provision differs from that computed at the federal statutory rate
Federal tax at the statutory rate (as a percent)	35.00%	35.00%	35.00%
State tax (net of federal benefits) (as a percent)	0.70%	0.72%	(1.84%)
Permanent items	0.27%	0.34%	3.49%
Tax credits	(0.96%)	(0.73%)	(1.03%)
Other (as a percent)	0.23%	(0.14%)	(2.80%)
Provision for income taxes as a percentage of pre-tax earnings	35.24%	35.19%	32.82%
Increase in capital from tax benefits for the employee stock-based compensation	$ 737	$ 865	$ 386
DEFERRED TAX ASSETS
Stock-based compensation	2,198	2,039
Compensation and benefits	1,113	1,033
Bad debt reserves	136	163
Accrued expenses	1,991	1,695
Fixed assets and depreciation	2,305	2,626
Base stock	6	10
State taxes	144	133
NOLs & credit carry-forwards	3,295	3,831
Deferred income tax asset	11,188	11,530
DEFERRED TAX LIABILITIES
Intangibles and amortization	(1,811)	(2,235)
Prepaid expenses	(1,365)	(1,279)
Real estate taxes	(154)	(150)
Other Reserves	(138)	(95)
Federal deduction on deferred state taxes	(366)	(356)
Deferred income tax liability	(3,834)	(4,115)
NET DEFERRED INCOME TAX ASSET	$ 7,354	$ 7,415