SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - $ / shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Basic (in shares)									16,948	16,734	16,302
Effect of dilutive stock options (in shares)									387	373	642
Diluted (in shares)									17,335	17,107	16,944
Per Share Amount
Basic (in dollars per share)	$ 0.30	$ 0.38	$ 0.30	$ 0.24	$ 0.23	$ 0.24	$ 0.18	$ 0.20	$ 1.22	$ 0.85	$ 1.10
Effect of dilutive stock options (in dollars per share)									(0.03)	(0.02)	(0.04)
Diluted (in dollars per share)	$ 0.29	$ 0.37	$ 0.29	$ 0.24	$ 0.22	$ 0.24	$ 0.18	$ 0.19	$ 1.19	$ 0.83	$ 1.06
Stock options
Anti-dilutive securities
Options to purchase shares of common stock									115,536	563,633	418,071
Exercise prices, low end of range (in dollars per share)									$ 23.09	$ 16.66	$ 21.65
Exercise prices, high end of range (in dollars per share)									$ 29.00	$ 29.00	$ 29.00