NET INCOME PER SHARE (DILUTED SHARES TABLE) (DETAILS) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Shares used in basic earnings per share calculation	45,856	45,838	45,662	45,950	46,386	47,081	47,873	48,368	45,826	47,423	48,370
Effect of dilutive securities:
Stock options									10	10	275
Restricted stock units									536	286	338
Performance-based restricted stock units									10	17	28
Total effects of dilutive securities									556	313	641
Shares used in dilutive earnings per share calculation	46,461	46,367	46,150	46,315	46,677	47,315	48,221	48,746	46,382	47,736	49,011