Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Weighted-average shares outstanding for basic and diluted net income per share
Net income (in dollars)	$ 15,691	$ 20,496	$ 31,188	$ 39,479
Basic net income per share:
Weighted-average shares outstanding - Basic	59,347	58,664	59,314	58,511
Basic net income per common share (in usd per share)	$ 0.26	$ 0.35	$ 0.53	$ 0.67
Diluted net income per share:
Weighted-average shares outstanding - Basic	59,347	58,664	59,314	58,511
Effect of potentially dilutive securities	39	341	72	391
Weighted-average shares outstanding - Diluted	59,386	59,005	59,386	58,902
Diluted net income per common share (in usd per share)	$ 0.26	$ 0.35	$ 0.53	$ 0.67