Computation of Earnings per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Basic earnings per share:
Numerator: Net income	$ 21,588	$ 33,999	$ 61,252	$ 72,636
Denominator:
Weighted-average common shares outstanding (in shares)	218,534,000	218,683,000	218,427,000	221,490,000
Basic earnings per share (in dollars per share)	$ 0.10	$ 0.16	$ 0.28	$ 0.33
Diluted earnings per share:
Numerator: Net income	$ 21,588	$ 33,999	$ 61,252	$ 72,636
Denominator:
Weighted-average common shares outstanding (in shares)	218,534,000	218,683,000	218,427,000	221,490,000
Dilutive effect of stock awards (in shares)	3,349,000	6,475,000	4,134,000	3,622,000
Total shares (in shares)	221,883,000	225,158,000	222,561,000	225,112,000
Diluted earnings per share (in dollars per share)	$ 0.10	$ 0.15	$ 0.28	$ 0.32
Anti-dilutive shares related to stock awards excluded from EPS calculation (in shares)	15,300,000	5,200,000	10,900,000	17,600,000