Summary of Changes in Stockholders' Equity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stockholders Equity Note [Line Items]
Balance at Beginning of Period			$ 696,170
Net Earnings	39,903	17,953	70,004	31,931
Balance at End of Period	764,320		764,320
Common Stock [Member]
Stockholders Equity Note [Line Items]
Balance at Beginning of Period			495
Stock Option Exercises			2
Balance at End of Period	497		497
Capital in Excess of Par Value [Member]
Stockholders Equity Note [Line Items]
Balance at Beginning of Period			224,053
Stock Compensation Expense			4,814
Shares Redeemed to Settle Employee Taxes			(435)
Stock Option Exercises			3,404
Balance at End of Period	231,836		231,836
Retained Earnings [Member]
Stockholders Equity Note [Line Items]
Balance at Beginning of Period			478,664
Dividends Declared to Stockholders			(9,949)
Net Earnings			70,004
Balance at End of Period	538,719		538,719
Accumulated Other Comprehensive Loss [Member]
Stockholders Equity Note [Line Items]
Balance at Beginning of Period			(7,042)
Change in Funded Status of Pension Plan, net of tax			310
Balance at End of Period	$ (6,732)		$ (6,732)