EARNINGS PER SHARE (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator for earnings per share:
Net income	$ 16,437	$ 14,065	$ 43,235	$ 39,485
Net income allocated to participating securities	0	0	0	(3,259)
Numerator for basic earnings per share	16,437	14,065	43,235	36,226
Effect on income available from reallocation of options	0	0	0	263
Numerator for diluted earnings per share	$ 16,437	$ 14,065	$ 43,235	$ 36,489
Denominator for basic earnings per share:
Weighted average shares outstanding (in shares)	46,162	42,952	45,492	38,990
Effect of dilutive securities (in shares):
Stock options	2,558	3,549	2,628	3,739
Denominator for diluted earnings per share (in shares)	48,720	46,501	48,120	42,729
Net income per share:
Basic (in dollars per share)	$ 0.36	$ 0.33	$ 0.95	$ 0.93
Diluted (in dollars per share)	$ 0.34	$ 0.30	$ 0.90	$ 0.85
Stock Options
Net income per share:
Anti-dilutive options not included in the calculation (in shares)	1,873	1,953	1,399	1,582