STOCK AWARD PLANS - Summary of Employee Stock Purchase Plan Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares purchased by employees (shares)	45,986
Aggregate cost to employees	$ 2,975
Expense recognized by the company	7,667	$ 4,841	$ 24,509	$ 30,626
Company expense on ESPP discount
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized by the company	$ 525	$ 491	$ 2,019	$ 2,040