Common Stock (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Mar. 29, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	May 02, 2019
Class of Stock [Line Items]
Maximum aggregate market value of potential common stock issuance	$ 150,000,000
Net proceeds to company		$ 25,879,000	$ 11,220,000	$ 369,061,000	$ 52,375,000
Common stock issued, amount		$ 27,389,000	10,395,000
Common stock available for issuance (in shares)		60,000,000		60,000,000
Equity Shelf Program
Class of Stock [Line Items]
Gross proceeds		$ 23,073,149	9,199,661	$ 99,023,464	50,976,456
Agent commissions		(230,731)	(91,997)	(990,234)	(509,765)
Net proceeds to company		$ 22,842,418	$ 9,107,664	$ 98,033,230	$ 50,466,691
Number of shares sold (in shares)		277,829	137,300	1,286,234	643,007
Weighted average price per share		$ 83.05	$ 67.00	$ 76.99	$ 79.28
Restricted Stock/Unit Plan, and Management Incentive Plan
Class of Stock [Line Items]
Common stock issued through Restricted Stock/Unit Plan, and Management Incentive Plan (in shares)		53,000
Dividend Reinvestment and Stock Purchase Plan
Class of Stock [Line Items]
Common stock issued through Restricted Stock/Unit Plan, and Management Incentive Plan (in shares)		34,000
Common stock issued, amount		$ 2,800,000
Subsequent Event
Class of Stock [Line Items]
Common stock available for issuance (in shares)						120,000,000