EMPLOYEE BENEFIT PLANS (Details) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended			6 Months Ended			6 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 number	Sep. 30, 2010	Mar. 31, 2011	Sep. 30, 2011 UK staff pension plan [Member]	Sep. 30, 2011 UK expatriate pension plan [Member]	Mar. 31, 2012 UK expatriate pension plan [Member]	Sep. 30, 2011 Norway pension plan [Member]	Mar. 31, 2012 Norway pension plan [Member]	Sep. 30, 2011 Plan 2007 [Member]	Sep. 30, 2011 Non-employee grants [Member]
Pension Plan [Line Items]
Service cost	$ 1,614,000	$ 1,334,000	$ 3,248,000	$ 2,612,000
Interest cost	7,122,000	6,658,000	14,334,000	13,040,000
Expected return on assets	(7,397,000)	(6,682,000)	(14,886,000)	(13,087,000)
Amortization of unrecognized losses	1,360,000	1,305,000	2,737,000	2,557,000
Net periodic pension cost	2,699,000	2,615,000	5,433,000	5,122,000
Cash Contributions						16,000,000	1,400,000		4,000,000
Estimated cash contributions								1,600,000		6,000,000
Incentive Compensation [Line Items]
Common Stock Shares reserved											2,400,000
Shares available for grant											823,940
Stock based compensation expense	2,300,000	4,300,000	7,480,000	8,019,000
Stock option grants- shares			259,521
Restricted stock grants- shares			183,384									18,199
Restricted stock grants- fair value			$ 44.13
Risk free interest rate			1.52%
Expected life (years)			6
Volatility			47.05%
Dividend yield			1.37%
Weighted average exercise price of options granted	$ 43.79		$ 43.79
Weighted average grant-date fair value of options granted			$ 17.32
Performance cash compensation liability	$ 4,700,000		$ 4,700,000		$ 1,700,000
Performance Cash Compensation Expense			Compensation expense (benefit) recorded related to the performance cash awards during the three months ended September 30, 2011 and 2010 was $(0.6) million and $0.3 million, respectively, and six months ended September 30, 2011 and 2010 was $3.0 million and $0.3 million, respectively.