STOCK-BASED COMPENSATION - Valuation Assumptions and Other Information (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Option valuation assumptions for options granted
Weighted average expected volatility for options granted (as a percent)	32.98%	35.54%	35.81%
Weighted average risk free rate (as a percent)	2.76%	1.83%	1.14%
Weighted average grant date fair value per share of options granted (in dollars per share)	$ 13.52	$ 11.92	$ 6.67
Total fair value of shares vested	$ 2,080	$ 1,324	$ 1,758
Total intrinsic value of options exercised	4,659	5,819	3,276
Cash received for all stock option exercises	2,354	5,813	2,934
Tax benefit realized from stock awards exercised	$ 978	$ 2,037	$ 1,146
Directors
Option valuation assumptions for options granted
Expected life	3 years 15 days	2 years 11 months 27 days	2 years 8 months 23 days
Executives
Option valuation assumptions for options granted
Expected life	5 years 26 days	5 years 18 days	4 years 8 months 16 days
Employees
Option valuation assumptions for options granted
Expected life	4 years 1 month 13 days	4 years 1 month 21 days	4 years 1 month 6 days