NET INCOME PER SHARE - Calculations of Basic and Diluted Net Income Per Share and Potential Common Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income	$ 17,629	$ 17,294	$ 40,338	$ 32,430
Denominator:
Denominator for basic net income per share - weighted average common shares outstanding (in shares)	41,206	41,425	41,128	41,417
Dilutive common equivalent shares:
Weighted average stock options (in shares)	7	43	11	63
Weighted average restricted stock units (in shares)	323	416	540	489
Denominator for diluted net income per share - weighted average shares outstanding (in shares)	41,536	41,884	41,679	41,969
Net income per share:
Basic net income per share (in USD per share)	$ 0.43	$ 0.42	$ 0.98	$ 0.78
Diluted net income per share (in USD per share)	$ 0.42	$ 0.41	$ 0.97	$ 0.77