NET INCOME PER SHARE (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended						12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Unvested Stock Awards Outstanding and Convertible Debt Securities [Member]	Mar. 31, 2011 Unvested Stock Awards Outstanding and Convertible Debt Securities [Member]	Mar. 31, 2012 Convertible Debt [Member]	Dec. 31, 2006 Convertible Debt 0.75 Percent Due September 2013 [Member]	Dec. 31, 2006 Convertible Debt Due in 2013 [Member]
Anti-dilutive Securities Excluded From Computation Of Earnings Per Share
Weighted average number of basic common shares outstanding (in shares)	49,827,000	49,319,000
Weighted average dilutive stock options, restricted stock, restricted stock units and performance share units (in shares)	607,000	1,217,000
Assumed conversion of convertible debt (in shares)	913,000	623,000
Weighted average number of diluted common and common equivalent shares outstanding (in shares)	51,347,000	51,159,000
Anti-dilutive potential common shares (in shares)			2,245,000	1,300,000	2,000,000
Debt Instrument Convertible Debt Hedge Transactions [Abstract]
Aggregate principal amount						$ 172.5
Number of shares the Company is entitled to purchase from Goldman Sachs and Merrill Lynch under hedge agreement (shares, in millions)							4,300,000
Convertible debt conversion price (in dollars per share)							$ 40.38
Number of shares Goldman Sachs and Merrill Lynch (the counterparties) are entitled to purchase from the Company under the hedge agreement (shares, in millions)							4,300,000
Counterparty strike price (in dollars per share)							$ 50.47