CAPITAL STOCK AND STOCK AWARD PLANS - Summary of Employee Stock Purchase Plan Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Purchased By Employees (in shares)	215,613	225,241	228,103
Aggregate Cost to Employees	$ 14,048	$ 14,032	$ 13,045
Expense Recognized By the Company	41,805	37,565	57,661
Company expense on ESPP discount
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense Recognized By the Company	$ 2,479	$ 2,475	$ 2,269