SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - $ / shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Basic (in shares)									17,305	16,948	16,734
Effect of dilutive stock options (in shares)									359	387	373
Diluted (in shares)									17,664	17,335	17,107
Per Share Amount
Basic (in dollars per share)	$ 0.37	$ 0.45	$ 0.33	$ 0.27	$ 0.30	$ 0.38	$ 0.30	$ 0.24	$ 1.42	$ 1.22	$ 0.85
Effect of dilutive stock options (in dollars per share)									(0.03)	(0.03)	(0.02)
Diluted (in dollars per share)	$ 0.36	$ 0.45	$ 0.32	$ 0.26	$ 0.29	$ 0.37	$ 0.29	$ 0.24	$ 1.39	$ 1.19	$ 0.83
Stock options
Anti-dilutive securities
Options to purchase shares of common stock									106,102	115,536	563,633
Exercise prices, low end of range (in dollars per share)									$ 28.02	$ 23.09	$ 16.66
Exercise prices, high end of range (in dollars per share)									$ 29.00	$ 29.00	$ 29.00