STOCK-BASED COMPENSATION - Valuation Assumptions and Other Information (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Option valuation assumptions for options granted
Expected volatility (as a percent)	35.54%	35.81%	39.10%
Weighted average risk free rate (as a percent)	1.83%	1.14%	1.14%
Weighted average grant date fair value per share of options granted (in dollars per share)	$ 11.92	$ 6.67	$ 5.90
Total fair value of shares vested	$ 1,324	$ 1,758	$ 1,041
Total intrinsic value of options exercised	5,819	3,276	4,321
Cash received for all stock option exercises	5,813	2,934	3,900
Tax benefit realized from stock awards exercised	$ 2,037	$ 1,146	$ 1,512
Directors
Option valuation assumptions for options granted
Expected life	2 years 11 months 27 days	2 years 8 months 23 days	3 years 11 months 19 days
Executives
Option valuation assumptions for options granted
Expected life	5 years 18 days	4 years 8 months 16 days	4 years 3 months 11 days
Employees
Option valuation assumptions for options granted
Expected life	4 years 1 month 21 days	4 years 1 month 6 days	3 years 11 months 19 days