Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Sep. 11, 2006	Apr. 30, 2016	Apr. 25, 2015	Apr. 26, 2014	Apr. 28, 2012	Dec. 31, 2002	Mar. 31, 2013	Dec. 31, 1991
Shareholders Equity [Line Items]
Common stock repurchased and retired, shares		4,379,000	1,194,000	2,354,000
Common stock repurchased and retired, value		$ 200,000	$ 47,539	$ 96,486
Average cost of common shares repurchased and retired (in usd per share)		$ 45.68	$ 39.81	$ 40.99
Shares authorized for repurchase under share repurchase program							25,000,000
Remaining shares available under repurchase program		16,497,000
Hours of service completed in order to be allocated shares of stock acquired by plan		1000 hours
ESOP share based compensation expense		$ 11,953	$ 9,939	$ 10,199
Number of shares allocated to ESOP		11,985,000
Number of shares allocated to ESOP, Fair value		$ 519,531
Fair value of unearned shares by ESOP		$ 68,916	$ 77,738
Minimum [Member]
Shareholders Equity [Line Items]
Unearned shares held by ESOP to occur over a period		5 years
Maximum [Member]
Shareholders Equity [Line Items]
Unearned shares held by ESOP to occur over a period		10 years
Unearned ESOP Shares [Member]
Shareholders Equity [Line Items]
Fair value of unearned shares by ESOP		$ 107,814
Thompson Dental Company [Member]
Shareholders Equity [Line Items]
Additional loan to ESOP						$ 12,612
ESOP acquiring shares during acquisition						666,000
Interest due from ESOP					$ 200
Total shares allocated to ESOP						98,000
Remaining shares in ESOP						568,000
Committed-to-be-released shares		10,000
Suspense shares		436,000
1990 Note [Member]
Shareholders Equity [Line Items]
ESOP company loan								$ 22,000
2006 Senior Notes [Member]
Shareholders Equity [Line Items]
ESOP company loan	$ 105,000
ESOP acquiring shares during acquisition	3,160,000				844,000
Contributed to ESOP					$ 20,214
Committed-to-be-released shares		259,000
Suspense shares		1,783,000