SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Weighted Average Shares Outstanding (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Weighted average number of shares outstanding – basic	32,559	32,142	32,791
Effect of dilutive securities:
Stock options	420	545	502
Non-vested stock and stock units	289	303	316
Weighted average number of shares outstanding – diluted	33,268	32,990	33,609
Anti-dilutive securities	25	117	50