Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Losses [Member]
Beginning balance at Mar. 31, 2012	$ 472,511	$ 453	$ 37,692	$ 439,882	$ (5,516)
Net Earnings	57,744			57,744
Net proceeds from Equity Offering	154,832	35	154,797
Stock Option Exercises and Restricted Share Vesting	19,645	8	19,637
Tax Benefit-Stock Option Exercise	6,493		6,493
Dividends to Stockholders	(18,962)			(18,962)
Stock Compensation Expense	9,002		9,002
Shares Redeemed to Settle Employee Taxes	(3,569)	(1)	(3,568)
Unfunded Pension Liability, net of tax	(1,526)				(1,526)
Ending Balance at Mar. 31, 2013	696,170	495	224,053	478,664	(7,042)
Net Earnings	124,243			124,243
Stock Option Exercises and Restricted Share Vesting	14,187	5	14,182
Tax Benefit-Stock Option Exercise	8,067		8,067
Dividends to Stockholders	(19,950)			(19,950)
Stock Compensation Expense	10,136	1	10,135
Shares Redeemed to Settle Employee Taxes	(2,913)		(2,913)
Unfunded Pension Liability, net of tax	1,559				1,559
Ending Balance at Mar. 31, 2014	831,499	501	253,524	582,957	(5,483)
Net Earnings	186,853			186,853
Stock Option Exercises and Restricted Share Vesting	4,311	1	4,310
Tax Benefit-Stock Option Exercise	5,743		5,743
Dividends to Stockholders	(20,093)			(20,093)
Stock Compensation Expense	13,030		13,030
Shares Redeemed to Settle Employee Taxes	(4,166)		(4,166)
Unfunded Pension Liability, net of tax	(6,584)				(6,584)
Ending Balance at Mar. 31, 2015	$ 1,010,593	$ 502	$ 272,441	$ 749,717	$ (12,067)