FAIR VALUE MEASUREMENTS - Summary of valuation of financial instruments measured at fair value on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Available-for-sale securities
Fair Value	$ 35,113	$ 37,484
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets, Level 1
Assets:
Trading securities
Available-for-sale securities
Total
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets, Level 1 | Municipal Obligations
Available-for-sale securities
Fair Value
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets, Level 1 | Corporate Obligations
Available-for-sale securities
Fair Value
Fair Value, Measurements, Recurring | Significant other observable inputs, Level 2
Assets:
Trading securities	$ 6,408	$ 6,575
Available-for-sale securities
Total	35,113	37,484
Fair Value, Measurements, Recurring | Significant other observable inputs, Level 2 | Municipal Obligations
Available-for-sale securities
Fair Value	30,098	32,080
Fair Value, Measurements, Recurring | Significant other observable inputs, Level 2 | Corporate Obligations
Available-for-sale securities
Fair Value	$ 5,015	$ 5,404
Fair Value, Measurements, Recurring | Significant unobservable inputs, Level 3
Assets:
Trading securities
Available-for-sale securities
Total
Fair Value, Measurements, Recurring | Significant unobservable inputs, Level 3 | Municipal Obligations
Available-for-sale securities
Fair Value
Fair Value, Measurements, Recurring | Significant unobservable inputs, Level 3 | Corporate Obligations
Available-for-sale securities
Fair Value